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1
Dubyak, George R. "Ion homeostasis, channels, and transporters: an update on cellular mechanisms." Advances in Physiology Education 28, no. 4 (December 2004): 143–54. http://dx.doi.org/10.1152/advan.00046.2004.
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The steady-state maintenance of highly asymmetric concentrations of the major inorganic cations and anions is a major function of both plasma membranes and the membranes of intracellular organelles. Homeostatic regulation of these ionic gradients is critical for most functions. Due to their charge, the movements of ions across biological membranes necessarily involves facilitation by intrinsic membrane transport proteins. The functional characterization and categorization of membrane transport proteins was a major focus of cell physiological research from the 1950s through the 1980s. On the basis of these functional analyses, ion transport proteins were broadly divided into two classes: channels and carrier-type transporters (which include exchangers, cotransporters, and ATP-driven ion pumps). Beginning in the mid-1980s, these functional analyses of ion transport and homeostasis were complemented by the cloning of genes encoding many ion channels and transporter proteins. Comparison of the predicted primary amino acid sequences and structures of functionally similar ion transport proteins facilitated their grouping within families and superfamilies of structurally related membrane proteins. Postgenomics research in ion transport biology increasingly involves two powerful approaches. One involves elucidation of the molecular structures, at the atomic level in some cases, of model ion transport proteins. The second uses the tools of cell biology to explore the cell-specific function or subcellular localization of ion transport proteins. This review will describe how these approaches have provided new, and sometimes surprising, insights regarding four major questions in current ion transporter research. 1) What are the fundamental differences between ion channels and ion transporters? 2) How does the interaction of an ion transport protein with so-called adapter proteins affect its subcellular localization or regulation by various intracellular signal transduction pathways? 3) How does the specific lipid composition of the local membrane microenvironment modulate the function of an ion transport protein? 4) How can the basic functional properties of a ubiquitously expressed ion transport protein vary depending on the cell type in which it is expressed?
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Martinez, J. R. "Ion Transport and Water Movement." Journal of Dental Research 66, no. 1_suppl (February 1987): 638–47. http://dx.doi.org/10.1177/00220345870660s106.
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Secretion of water and electrolytes in salivary glands occurs by a dual process involving the formation of a plasma-like, isotonic primary-secretion in salivary acini and its subsequent modification in salivary-ducts by the removal and addition of specific ions. The mechanisms underlying the formation of primary acinar secretion have been investigated with a number of experimental approaches such as electrophysiology, the measurement of ion transport in gland fragments and dispersed acinar cells, and the evaluation of the ionic requirements for secretion in isolated, perfused gland preparations. The accumulated evidence suggests that salivary secretion is formed by a complex interaction between passive and active ion movements across acinar cell membranes, resulting in the trans-acinar movement of CI and Na+ and, by the osmotic gradient which develops, of water. A major consequence of stimulation is the release of K + through Ca++ -and voltage-sensitive channels and its subsequent recycling back into the cells by ouabain- and furosemide-sensitive transport systems. This results in NaCl uptake across the basolateral cell membrane and the subsequent efflux of CI through luminal membrane channels, which also appear to be sensitive to cellular Ca + +. The rates of these various ion movements appear to be, therefore, closely linked and interdependent. Ductal modification of the primary secretion has been studied in microperfused duct preparations. The evidence likewise indicates that it involves interactions between complex conductance pathways in the luminal cell membrane and a Na, K pump present in the basolateral cell membrane and that it is under autonomic and hormonal control. Activation of ductal transport mechanisms results in NaCl reabsorption and KHCO3 secretion. Final saliva thus differs from primary secretion in electrolyte composition and, because water permeability is low in the duct epithelium, becomes hypotonic. Alterations in fluid and electrolyte secretion such as those observed in disease can result, therefore, from disturbances in one or more of these complex transport processes in acinar or duct cells.
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Martinez, J. R. "Ion Transport and Water Movement." Journal of Dental Research 66, no. 2_suppl (February 1987): 638–47. http://dx.doi.org/10.1177/00220345870660s206.
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Secretion of water and electrolytes in salivary glands occurs by a dual process involving the formation of a plasma-like, isotonic primary-secretion in salivary acini and its subsequent modification in salivary-ducts by the removal and addition of specific ions. The mechanisms underlying the formation of primary acinar secretion have been investigated with a number of experimental approaches such as electrophysiology, the measurement of ion transport in gland fragments and dispersed acinar cells, and the evaluation of the ionic requirements for secretion in isolated, perfused gland preparations. The ac-cumulated evidence suggests that salivary secretion is formed by a complex interaction between passive and active ion movements across acinar cell membranes, resulting in the trans-acinar movement of Cl and Na* and, by the osmotic gradient which develops, of water. A major consequence of stimulation is the release of K+ through Ca++ -and voltage-sensitive channels and its subsequent recycling back into the cells by ouabain- and furosemide-sensitive transport systems. This results in NaCl uptake across the basolateral cell membrane and the subsequent efflux of Cl through luminal membrane channels, which also appear to be sensitive to cellular Ca++. The rates of these various ion movements appear to be, therefore, closely linked and interdependent. Ductal modification of the primary secretion has been studied in microperfused duct preparations. The evidence likewise indicates that it involves interactions between complex conductance pathways in the luminal cell membrane and a Na, K pump present in the basolateral cell membrane and that it is under autonomic and hormonal control. Activation of ductal transport mechanisms results in NaCl reabsorption and KHCO3 secretion. Final saliva thus differs from primary secretion in electrolyte composition and, because water permeability is low in the duct epithelium, becomes hypotonic. Alterations in fluid and electrolyte secretion such as those observed in disease can result, therefore, from disturbances in one or more of these complex transport processes in acinar or duct cells.
4
Brône, Bert, and Jan Eggermont. "PDZ proteins retain and regulate membrane transporters in polarized epithelial cell membranes." American Journal of Physiology-Cell Physiology 288, no. 1 (January 2005): C20—C29. http://dx.doi.org/10.1152/ajpcell.00368.2004.
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PDZ proteins retain and regulate membrane transporters in polarized epithelial cell membranes. Am J Physiol Cell Physiol 288: C20–C29, 2005; doi:10.1152/ajpcell.00368.2004.—The plasma membrane of epithelial cells is subdivided into two physically separated compartments known as the apical and basolateral membranes. To obtain directional transepithelial solute transport, membrane transporters (i.e., ion channels, cotransporters, exchangers, and ion pumps) need to be targeted selectively to either of these membrane domains. In addition, the transport properties of an epithelial cell will be maintained only if these membrane transporters are retained and properly regulated in their specific membrane compartments. Recent reports have indicated that PDZ domain-containing proteins play a dual role in these processes and, in addition, that different apical and basolateral PDZ proteins perform similar tasks in their respective membrane domains. First, although PDZ-based interactions are dispensable for the biosynthetic targeting to the proper membrane domain, the PDZ network ensures that the membrane proteins are efficiently retained at the cell surface. Second, the close spatial positioning of functionally related proteins (e.g., receptors, kinases, channels) into a signal transduction complex (transducisome) allows fast and efficient control of membrane transport processes.
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Bianchi, G. "Ion transport across blood cell membrane in essential hypertension." Current Opinion in Cardiology 1, no. 5 (September 1986): 634–40. http://dx.doi.org/10.1097/00001573-198609000-00009.
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Shennan, D. B., and C. A. R. Boyd. "Ion transport by the placenta: a review of membrane transport systems." Biochimica et Biophysica Acta (BBA) - Reviews on Biomembranes 906, no. 3 (October 1987): 437–57. http://dx.doi.org/10.1016/0304-4157(87)90019-0.
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Kourie, Joseph I. "Interaction of reactive oxygen species with ion transport mechanisms." American Journal of Physiology-Cell Physiology 275, no. 1 (July 1, 1998): C1—C24. http://dx.doi.org/10.1152/ajpcell.1998.275.1.c1.
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The use of electrophysiological and molecular biology techniques has shed light on reactive oxygen species (ROS)-induced impairment of surface and internal membranes that control cellular signaling. These deleterious effects of ROS are due to their interaction with various ion transport proteins underlying the transmembrane signal transduction, namely, 1) ion channels, such as Ca2+ channels (including voltage-sensitive L-type Ca2+currents, dihydropyridine receptor voltage sensors, ryanodine receptor Ca2+-release channels, andd- myo-inositol 1,4,5-trisphosphate receptor Ca2+-release channels), K+ channels (such as Ca2+-activated K+ channels, inward and outward K+ currents, and ATP-sensitive K+ channels), Na+ channels, and Cl− channels; 2) ion pumps, such as sarcoplasmic reticulum and sarcolemmal Ca2+pumps, Na+-K+-ATPase (Na+ pump), and H+-ATPase (H+ pump); 3) ion exchangers such as the Na+/Ca2+exchanger and Na+/H+exchanger; and 4) ion cotransporters such as K+-Cl−, Na+-K+-Cl−, and Pi-Na+cotransporters. The mechanism of ROS-induced modifications in ion transport pathways involves 1) oxidation of sulfhydryl groups located on the ion transport proteins, 2) peroxidation of membrane phospholipids, and 3) inhibition of membrane-bound regulatory enzymes and modification of the oxidative phosphorylation and ATP levels. Alterations in the ion transport mechanisms lead to changes in a second messenger system, primarily Ca2+ homeostasis, which further augment the abnormal electrical activity and distortion of signal transduction, causing cell dysfunction, which underlies pathological conditions.
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Morachevskaya, Elena A., and Anastasia V. Sudarikova. "Actin dynamics as critical ion channel regulator: ENaC and Piezo in focus." American Journal of Physiology-Cell Physiology 320, no. 5 (May 1, 2021): C696—C702. http://dx.doi.org/10.1152/ajpcell.00368.2020.
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Ion channels in plasma membrane play a principal role in different physiological processes, including cell volume regulation, signal transduction, and modulation of membrane potential in living cells. Actin-based cytoskeleton, which exists in a dynamic balance between monomeric and polymeric forms (globular and fibrillar actin), can be directly or indirectly involved in various cellular responses including modulation of ion channel activity. In this mini-review, we present an overview of the role of submembranous actin dynamics in the regulation of ion channels in excitable and nonexcitable cells. Special attention is focused on the important data about the involvement of actin assembly/disassembly and some actin-binding proteins in the control of the epithelial Na+ channel (ENaC) and mechanosensitive Piezo channels whose integral activity has a potential impact on membrane transport and multiple coupled cellular reactions. Growing evidence suggests that actin elements of the cytoskeleton can represent a “converging point” of various signaling pathways modulating the activity of ion transport proteins in cell membranes.
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Bing, Robert F., Anthony M. Heagerty, Herbert Thurston, and John D. Swales. "Ion transport in hypertension: are changes in the cell membrane responsible?" Clinical Science 71, no. 3 (September 1, 1986): 225–30. http://dx.doi.org/10.1042/cs0710225.
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Disturbances in several, distinct cell membrane ion transport processes have been demonstrated in essential hypertension but their variable relationship to blood pressure in different populations has made it difficult to achieve a unifying hypothesis. We suggest that altered composition of the lipid fraction of the cell membrane is the common underlying factor. This would produce many of the reported perturbations of cell membrane properties and function, not all of which relate directly to the development of hypertension, but which act as markers for the underlying abnormality. However, functions such as phosphoinositol turnover, calcium binding and Ca2+,Mg2+-ATPase dependent calcium efflux, which are influenced by the lipid composition of the membrane, provide a possible link between the membrane disturbance, intracellular calcium, vascular smooth muscle contraction and blood pressure. Alteration in the lipid content of the cell membrane not only provides an explanation for the variability in the ion transport abnormalities between populations but perhaps also for some of the variability in blood pressure within a single population. It also provides a potential means of influencing blood pressure by dietary intervention.
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Muallem, Shmuel, Woo Young Chung, Archana Jha, and Malini Ahuja. "Lipids at membrane contact sites: cell signaling and ion transport." EMBO reports 18, no. 11 (October 13, 2017): 1893–904. http://dx.doi.org/10.15252/embr.201744331.
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Kirk, Kiaran. "Membrane Transport in the Malaria-Infected Erythrocyte." Physiological Reviews 81, no. 2 (April 1, 2001): 495–537. http://dx.doi.org/10.1152/physrev.2001.81.2.495.
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The malaria parasite is a unicellular eukaryotic organism which, during the course of its complex life cycle, invades the red blood cells of its vertebrate host. As it grows and multiplies within its host blood cell, the parasite modifies the membrane permeability and cytosolic composition of the host cell. The intracellular parasite is enclosed within a so-called parasitophorous vacuolar membrane, tubular extensions of which radiate out into the host cell compartment. Like all eukaryote cells, the parasite has at its surface a plasma membrane, as well as having a variety of internal membrane-bound organelles that perform a range of functions. This review focuses on the transport properties of the different membranes of the malaria-infected erythrocyte, as well as on the role played by the various membrane transport systems in the uptake of solutes from the extracellular medium, the disposal of metabolic wastes, and the origin and maintenance of electrochemical ion gradients. Such systems are of considerable interest from the point of view of antimalarial chemotherapy, both as drug targets in their own right and as routes for targeting cytotoxic agents into the intracellular parasite.
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HAMM-ALVAREZ, SARAH F., and MICHAEL P. SHEETZ. "Microtubule-Dependent Vesicle Transport: Modulation of Channel and Transporter Activity in Liver and Kidney." Physiological Reviews 78, no. 4 (October 1, 1998): 1109–29. http://dx.doi.org/10.1152/physrev.1998.78.4.1109.
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Hamm-Alvarez, Sarah F., and Michael P. Sheetz. Microtubule-Dependent Vesicle Transport: Modulation of Channel and Transporter Activity in Liver and Kidney. Physiol. Rev. 78: 1109–1129, 1998. — Microtubule-based vesicle transport driven by kinesin and cytoplasmic dynein motor proteins facilitates several membrane-trafficking steps including elements of endocytosis and exocytosis in many different cell types. Most early studies on the role of microtubule-dependent vesicle transport in membrane trafficking focused either on neurons or on simple cell lines. More recently, other work has considered the role of microtubule-based vesicle transport in other physiological systems, including kidney and liver. Investigation of the role of microtubule-based vesicle transport in membrane trafficking in cells of the kidney and liver suggests a major role for microtubule-based vesicle transport in the rapid and directed movement of ion channels and transporters to and from the apical plasma membranes, events essential for kidney and liver function and homeostasis. This review discusses the evidence supporting a role for microtubule-based vesicle transport and the motor proteins, kinesin and cytoplasmic dynein, in different aspects of membrane trafficking in cells of the kidney and liver, with emphasis on those functions such as maintenance of ion channel and transporter composition in apical membranes that are specialized functions of these organs. Evidence that defects in microtubule-based transport contribute to diseases of the kidney and liver is also discussed.
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Karle, Christoph, Tobias Gehrig, Ralf Wodopia, Sabine Höschele, Volker A. W. Kreye, Hugo A. Katus, Peter Bärtsch, and Heimo Mairbäurl. "Hypoxia-induced inhibition of whole cell membrane currents and ion transport of A549 cells." American Journal of Physiology-Lung Cellular and Molecular Physiology 286, no. 6 (June 2004): L1154—L1160. http://dx.doi.org/10.1152/ajplung.00403.2002.
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In excitable cells, hypoxia inhibits K channels, causes membrane depolarization, and initiates complex adaptive mechanisms. It is unclear whether K channels of alveolar epithelial cells reveal a similar response to hypoxia. A549 cells were exposed to hypoxia during whole cell patch-clamp measurements. Hypoxia reversibly inhibited a voltage-dependent outward current, consistent with a K current, because tetraethylamonium (TEA; 10 mM) abolished this effect; however, iberiotoxin (0.1 μM) does not. In normoxia, TEA and iberiotoxin inhibited whole cell current (−35%), whereas the K-channel inhibitors glibenclamide (1 μM), barium (1 mM), chromanol B293 (10 μM), and 4-aminopyridine (1 mM) were ineffective. 86Rb uptake was measured to see whether K-channel modulation also affected transport activity. TEA, iberiotoxin, and 4-h hypoxia (1.5% O2) inhibited total 86Rb uptake by 40, 20, and 35%, respectively. Increased extracellular K also inhibited 86Rb uptake in a dose-dependent way. The K-channel opener 1-ethyl-2-benzimidazolinone (1 mM) increased 86Rb uptake by 120% in normoxic and hypoxic cells by activation of Na-K pumps (+60%) and Na-K-2Cl cotransport (+170%). However, hypoxic transport inhibition was also seen in the presence of 1-ethyl-2-benzimidazolinone, TEA, and iberiotoxin. These results indicate that hypoxia, membrane depolarization, and K-channel inhibition decrease whole cell membrane currents and transport activity. It appears, therefore, that a hypoxia-induced change in membrane conductance and membrane potential might be a link between hypoxia and alveolar ion transport inhibition.
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Guggino, W. B., H. Oberleithner, and G. Giebisch. "Relationship between cell volume and ion transport in the early distal tubule of the Amphiuma kidney." Journal of General Physiology 86, no. 1 (July 1, 1985): 31–58. http://dx.doi.org/10.1085/jgp.86.1.31.
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The roles of apical and basolateral transport mechanisms in the regulation of cell volume and the hydraulic water permeabilities (Lp) of the individual cell membranes of the Amphiuma early distal tubule (diluting segment) were evaluated using video and optical techniques as well as conventional and Cl-sensitive microelectrodes. The Lp of the apical cell membrane calculated per square centimeter of tubule is less than 3% that of the basolateral cell membrane. Calculated per square centimeter of membrane, the Lp of the apical cell membrane is less than 40% that of the basolateral cell membrane. Thus, two factors are responsible for the asymmetry in the Lp of the early distal tubule: an intrinsic difference in the Lp per square centimeter of membrane area, and a difference in the surface areas of the apical and basolateral cell membranes. Early distal tubule cells do not regulate volume after a reduction in bath osmolality. This cell swelling occurs without a change in the intracellular Cl content or the basolateral cell membrane potential. In contrast, reducing the osmolality of the basolateral solution in the presence of luminal furosemide diminishes the magnitude of the increase in cell volume to a value below that predicted from the change in osmolality. This osmotic swelling is associated with a reduction in the intracellular Cl content. Hence, early distal tubule cells can lose solute in response to osmotic swelling, but only after the apical Na/K/Cl transporter is blocked. Inhibition of basolateral Na/K ATPase with ouabain results in severe cell swelling. This swelling in response to ouabain can be inhibited by the prior application of furosemide, which suggests that the swelling is due to the continued entry of solutes, primarily through the apical cotransport pathway.
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Radenovic, Cedomir, Milos Beljanski, Georgij Maksimov, Aleksandar Kalauzi, and Milan Drazic. "The mechanism of the NH4 ion oscillatory transport across the excitable cell membrane." Zbornik Matice srpske za prirodne nauke, no. 109 (2005): 5–19. http://dx.doi.org/10.2298/zmspn0519005r.
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This paper presents results on typical oscillations of the membrane potential induced by the excitation of the cell membrane by different concentrations of the NH4Cl solution. The existence of four classes of oscillations of the membrane potential and several different single and local impulses rhythmically occurring were determined. It is known that the oscillatory processes of the membrane potential are in direct dependence on oscillatory transport processes of NH4 and Cl ions across the excitable cell membrane. A hypothesis on a possible mechanism of oscillatory transport processes of NH4 and Cl ions across the excitable cell membrane is also presented.
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Soybel, D. I., M. B. Davis, and L. Y. Cheung. "Characteristics of basolateral Cl- transport by gastric surface epithelium in Necturus antral mucosa." American Journal of Physiology-Gastrointestinal and Liver Physiology 264, no. 5 (May 1, 1993): G910—G920. http://dx.doi.org/10.1152/ajpgi.1993.264.5.g910.
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Conventional and ion-selective microelectrodes were used to characterize transport of Cl- across the basolateral cell membranes of gastric surface epithelium in isolated preparations of gastric antrum of Necturus. Conventional, voltage-sensing electrodes were used to evaluate changes in membrane potentials and resistances during removal of Cl- from the nutrient perfusate. Liquid ion exchanger Cl(-)-selective microelectrodes were constructed and validated to measure intracellular Cl- activity (aiCl). Our data indicate that 1) aiCl (range 12-25 mM) is close to that predicted if Cl- is distributed across the cell membranes by electrochemical equilibrium, 2) aiCl is not influenced by changes in luminal Cl- content but is susceptible to changes in nutrient Cl- content, 3) Cl- conductances cannot be detected in the basolateral membrane and changes in membrane potentials do not influence aiCl, and 4) Cl- accumulation across the basolateral membrane depends on Na+ and the level of [K+] in the nutrient solution. Inhibition of K(+)-dependent Cl- accumulation, in the absence of nutrient Na+ or in the presence of the inhibitor bumetanide, was demonstrated. These findings suggest that basolateral Na(+)-K(+)-Cl- cotransport is important in regulating cell Cl- levels in surface cells of the gastric antrum in Necturus.
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Sakaguchi, T., G. P. Leser, and R. A. Lamb. "The ion channel activity of the influenza virus M2 protein affects transport through the Golgi apparatus." Journal of Cell Biology 133, no. 4 (May 15, 1996): 733–47. http://dx.doi.org/10.1083/jcb.133.4.733.
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High level expression of the M2 ion channel protein of influenza virus inhibits the rate of intracellular transport of the influenza virus hemagglutinin (HA) and that of other integral membrane glycoproteins. HA coexpressed with M2 is properly folded, is not associated with GRP78-BiP, and trimerizes with the same kinetics as when HA is expressed alone. Analysis of the rate of transport of HA from the ER to the cis and medial golgi compartments and the TGN indicated that transport through the Golgi apparatus is delayed. Uncleaved HA0 was not expressed at the cell surface, and accumulation HA at the plasma membrane was reduced to 75-80% of control cells. The delay in intracellular transport of HA on coexpression of M2 was not observed in the presence of the M2-specific ion channel blocker, amantadine, indicating that the Golgi transport delay is due to the M2 protein ion channel activity equilibrating pH between the Golgi lumen and the cytoplasm, and not due to saturation of the intracellular transport machinery. The Na+/H+ ionophore, monensin, which also equilibrates pH between the Golgi lumen and the cytoplasm, caused a similar inhibition of intracellular transport as M2 protein expression did for HA and other integral membrane glycoproteins. EM data showed a dilation of Golgi cisternae in cells expressing the M2 ion channel protein. Taken together, the data suggest a similarity of effects of M2 ion channel activity and monensin on intracellular transport through the Golgi apparatus.
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Shennan, David B. "K+ and Cl− transport by mammary secretory cell apical membrane vesicles isolated from milk." Journal of Dairy Research 59, no. 3 (August 1992): 339–48. http://dx.doi.org/10.1017/s0022029900030612.
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SummaryThe transport of K+ (Rb+) and Cl− by membrane vesicles isolated from bovine milk has been studied using ion-exchange column chromatography. K+ (Rb+) and Cl− accumulation by the vesicles was time-dependent and was almost abolished by 0·1% Triton X-100, suggesting that uptake represents ‘real’ transport rather than binding. K+ (Rb+) uptake was influenced by the anion in solution in a manner suggesting that influx is sensitive to changes in vesicle membrane potential. Similarly, Cl− uptake was found to be sensitive to vesicle electrical potential: Cl− influx was enhanced by inside positive potentials. Cl− uptake was not saturable with respect to external Cl−. The results suggest that K+ (Rb+) and Cl− cross the apical membrane by way of conductance pathways. The similarity between ion transport by skim milk membrane vesicles and that of the apical aspect of the intact mammary epithelium suggests that the former may be a good model to study solute transport by the apical membrane of mammary secretory cells.
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Stanton, B. A., and B. Kaissling. "Regulation of renal ion transport and cell growth by sodium." American Journal of Physiology-Renal Physiology 257, no. 1 (July 1, 1989): F1—F10. http://dx.doi.org/10.1152/ajprenal.1989.257.1.f1.
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Intracellular sodium has been implicated in a variety of cellular processes including regulation of Na+-K+-ATPase activity, mitogen-induced cell growth, and proliferation and stimulation of Na+-K+-ATPase by aldosterone. In renal epithelial cells a rise in sodium uptake across the apical membrane increases intracellular sodium concentration, which in turn stimulates the turnover rate of Na+-K+-ATPase and thereby enhances sodium efflux across the basolateral membrane. A prolonged increase in sodium uptake causes dramatic hypertrophy and hyperplasia and a rise in the quantity of Na+-K+-ATPase in the basolateral membrane. These structural and functional changes occur in the kidney in the absence of alterations in plasma aldosterone and vasopressin levels. Several mitogens induce growth and proliferation by initiating a cascade of events, which include a rise in intracellular sodium. Accordingly, an increase in the sodium concentration within renal epithelial cells may elicit a “mitogen-like” effect by initiating the cascade at the sodium step, even in the absence of a mitogen. A rise in cell sodium may also stimulate the production of autocrine growth factors that directly or indirectly regulate cell growth and proliferation, by modifying the response to mitogens or to changes in the ionic composition of the extracellular fluid. In this review we will examine the evidence that supports a role for intracellular sodium in regulating these cellular events in renal epithelial cells.
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Wolosin, J. M. "Ion transport studies with H+-K+-ATPase-rich vesicles: implications for HCl secretion and parietal cell physiology." American Journal of Physiology-Gastrointestinal and Liver Physiology 248, no. 6 (June 1, 1985): G595—G607. http://dx.doi.org/10.1152/ajpgi.1985.248.6.g595.
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A summary of recent studies on relations between the properties of the membrane incorporating the H+-K+-ATPase, the H+ motive force in gastric acid secretion, and the secretory state of the parietal cell is presented. Depending on tissue secretory state, two distinct H+-K+-ATPase-rich membranes predominate in tissue homogenates, the gastric microsomes derived from the intracellular tubulovesicles of the resting cell and the stimulation-associated (SA) vesicle derived from the apical membrane of the acid-secreting cell. Structural and chemical differences between both vesicular types lend support to the notion that the formation of an expanded, elaborated apical membrane in the secreting parietal cell results from fusion of tubulovesicles containing the H+-K+-ATPase to an apical membrane of different chemical composition. Comparison of polypeptide composition of microsomes and SA membranes provides a way to identify and isolate membrane and cytoskeletal components putatively involved in the membrane interconversion process. Comparison of transport properties between gastric microsomes and SA vesicles demonstrates that stimulation triggers the appearance of rapid K+ and Cl- permeabilities in the H+-K+-ATPase membrane, allowing efficient acid accumulation in SA vesicles by the combination of rapid KCl influx followed by ATPase-driven H+ for K+ exchange, i.e., by K+ recycling. These stimulation-triggered conductances are functionally independent. Nevertheless, their concurrent inhibition by certain divalent cations (Mn2+,Zn2+) suggests their location within a single physical domain. The compatibility of the K+-recycling model for HCl accumulation in SA vesicles with gastric HCl secretion and selected electrophysiological observations and certain implications of the findings for cellular mechanisms of transport regulation in the context of a membrane fusion and recycling model are discussed.
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Heiny, Judith A., Stephen C. Cannon, and Marino DiFranco. "A four-electrode method to study dynamics of ion activity and transport in skeletal muscle fibers." Journal of General Physiology 151, no. 9 (July 18, 2019): 1146–55. http://dx.doi.org/10.1085/jgp.201912398.
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Ion movements across biological membranes, driven by electrochemical gradients or active transport mechanisms, control essential cell functions. Membrane ion movements can manifest as electrogenic currents or electroneutral fluxes, and either process can alter the extracellular and/or intracellular concentration of the transported ions. Classic electrophysiological methods allow accurate measurement of membrane ion movements when the transport mechanism produces a net ionic current; however, they cannot directly measure electroneutral fluxes and do not detect any accompanying change in intracellular ion concentrations. Here, we developed a method for simultaneously measuring ion movements and the accompanying dynamic changes in intracellular ion concentrations in intact skeletal muscle fibers under voltage or current clamp in real time. The method combines a two-microelectrode voltage clamp with ion-selective and reference microelectrodes (four-electrode system). We validate the electrical stability of the system and the viability of the preparation for periods of ∼1 h. We demonstrate the power of this method with measurements of intracellular Cl−, H+, and Na+ to show (a) voltage-dependent redistribution of Cl− ions; (b) intracellular pH changes induced by changes in extracellular pCO2; and (c) electroneutral and electrogenic Na+ movements controlled by the Na,K-ATPase. The method is useful for studying a range of transport mechanisms in many cell types, particularly when the transmembrane ion movements are electrically silent and/or when the transport activity measurably changes the intracellular activity of a transported ion.
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López-Chàvez, Ernesto, Misael Solorza-Guzmàn, and Fray de Landa Castillo-Alvarado. "Molecular Simulation of Ion-Transport inside Chitosan Membranes." Advances in Science and Technology 46 (October 2006): 188–98. http://dx.doi.org/10.4028/www.scientific.net/ast.46.188.
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We have presented general ideas to develop a theoretical methodology, based on Molecular simulation and Einstein equation aimed to describe the mechanism and behavior of chitosan-membrane ion conductivity and to obtain its magnitude for different ionic species. Atomistic molecular modelling has been utilized to construct an ionic-conducting polymer electrolyte system consisting of poly(chitosan), H O 2 molecules, and + H O 3 , − OH , 2− 4 SO ions, inside of the simulation cell. The COMPASS force field was used. The simulation allows describing the mechanism of ionic conductivity along the polymer matrix. The theoretical results obtained are compared with previously-reported experimental data for chitosan membranes. The present methodology can be considered as a first step towards understanding these complex problems of technological interest.
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Garten, Matthias, Lars D. Mosgaard, Thomas Bornschlögl, Stéphane Dieudonné, Patricia Bassereau, and Gilman E. S. Toombes. "Whole-GUV patch-clamping." Proceedings of the National Academy of Sciences 114, no. 2 (December 21, 2016): 328–33. http://dx.doi.org/10.1073/pnas.1609142114.
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Studying how the membrane modulates ion channel and transporter activity is challenging because cells actively regulate membrane properties, whereas existing in vitro systems have limitations, such as residual solvent and unphysiologically high membrane tension. Cell-sized giant unilamellar vesicles (GUVs) would be ideal for in vitro electrophysiology, but efforts to measure the membrane current of intact GUVs have been unsuccessful. In this work, two challenges for obtaining the “whole-GUV” patch-clamp configuration were identified and resolved. First, unless the patch pipette and GUV pressures are precisely matched in the GUV-attached configuration, breaking the patch membrane also ruptures the GUV. Second, GUVs shrink irreversibly because the membrane/glass adhesion creating the high-resistance seal (>1 GΩ) continuously pulls membrane into the pipette. In contrast, for cell-derived giant plasma membrane vesicles (GPMVs), breaking the patch membrane allows the GPMV contents to passivate the pipette surface, thereby dynamically blocking membrane spreading in the whole-GMPV mode. To mimic this dynamic passivation mechanism, beta-casein was encapsulated into GUVs, yielding a stable, high-resistance, whole-GUV configuration for a range of membrane compositions. Specific membrane capacitance measurements confirmed that the membranes were truly solvent-free and that membrane tension could be controlled over a physiological range. Finally, the potential for ion transport studies was tested using the model ion channel, gramicidin, and voltage-clamp fluorometry measurements were performed with a voltage-dependent fluorophore/quencher pair. Whole-GUV patch-clamping allows ion transport and other voltage-dependent processes to be studied while controlling membrane composition, tension, and shape.
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Cragg, Peter J. "Artificial Transmembrane Channels for Sodium and Potassium." Science Progress 85, no. 3 (August 2002): 219–41. http://dx.doi.org/10.3184/003685002783238780.
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Transport of alkali metals, particularly sodium and potassium, across cell membranes is an essential function performed by special proteins that enable cells to regulate inter- and extracellular ion concentrations with exceptional selectivity. The importance of these channel-forming proteins has led to researchers emulating of their structural features: an ion-specific filter and conduction at rates up to 108 ions per second. Synthetic helical and cyclic polypeptides form channels, however, the specificity of ion transport is often low. Ion-specific macrocycles have been used as filters from which membrane-spanning derivatives have been prepared. Success has been limited as many compounds act as ion carriers rather than forming transmembrane channels. Surfactant compounds also allow ions to cross membranes but any specificity is serendipitous. Overall it seems possible to mimic either ion specificity or efficient transmembrane ion transport. The goal for the future will be to combine both characteristics in one artificial system.
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Yaroslavtsev, A. B., I. A. Stenina, and D. V. Golubenko. "Membrane materials for energy production and storage." Pure and Applied Chemistry 92, no. 7 (July 28, 2020): 1147–57. http://dx.doi.org/10.1515/pac-2019-1208.
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AbstractIon exchange membranes are widely used in chemical power sources, including fuel cells, redox batteries, reverse electrodialysis devices and lithium-ion batteries. The general requirements for them are high ionic conductivity and selectivity of transport processes. Heterogeneous membranes are much cheaper but less selective due to the secondary porosity with large pore size. The composition of grafted membranes is almost identical to heterogeneous ones. But they are more selective due to the lack of secondary porosity. The conductivity of ion exchange membranes can be improved by their modification via nanoparticle incorporation. Hybrid membranes exhibit suppressed transport of co-ions and fuel gases. Highly selective composite membranes can be synthesized by incorporating nanoparticles with modified surface. Furthermore, the increase in the conductivity of hybrid membranes at low humidity is a significant advantage for fuel cell application. Proton-conducting membranes in the lithium form intercalated with aprotic solvents can be used in lithium-ion batteries and make them more safe. In this review, we summarize recent progress in the synthesis, and modification and transport properties of ion exchange membranes, their transport properties, methods of preparation and modification. Their application in fuel cells, reverse electrodialysis devices and lithium-ion batteries is also reviewed.
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Lang, F., G. Messner, and W. Rehwald. "Electrophysiology of sodium-coupled transport in proximal renal tubules." American Journal of Physiology-Renal Physiology 250, no. 6 (June 1, 1986): F953—F962. http://dx.doi.org/10.1152/ajprenal.1986.250.6.f953.
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Effects of sodium-coupled transport on intracellular electrolytes and electrical properties of proximal renal tubule cells are described in this review. Simultaneous with addition of substrate for sodium-coupled transport to luminal perfusates, both cell membranes depolarize. The luminal cell membrane depolarizes due to opening of sodium-cotransport pathways. The depolarization of the peritubular cell membrane during sodium-coupled transport is primarily due to a circular current reentering the lumen via the paracellular pathway. The depolarization leads to a transient decrease of basolateral potassium conductance that in turn amplifies the depolarization. However, within 5-10 min of continued exposure to substrate, potassium conductance increases again, and peritubular cell membrane repolarizes. During depolarization the driving force of peritubular bicarbonate exit is reduced. As a result net alkalinization of the cell prevails despite an increase of intracellular sodium activity, which reduces the driving force for the sodium-hydrogen ion exchanger and would thus have been expected to acidify the cell. No evidence is obtained for regulatory inhibition of sodium-coupled transport by intracellular sodium or calcium. Rather, luminal cotransport is altered by the change of driving forces.
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Stewart, GW, BE Hepworth-Jones, JN Keen, BC Dash, AC Argent, and CM Casimir. "Isolation of cDNA coding for an ubiquitous membrane protein deficient in high Na+, low K+ stomatocytic erythrocytes." Blood 79, no. 6 (March 15, 1992): 1593–601. http://dx.doi.org/10.1182/blood.v79.6.1593.1593.
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Abstract Human red blood cells (RBCs) that are deficient in an integral membrane- associated protein (“stomatin“) of apparent molecular mass 31 Kd show a catastrophic increase in passive membrane permeability to the univalent cations Na+ and K+ and are stomatocytic in shape. We have purified this protein from normal RBC membranes and isolated a cDNA clone coding for it. The deduced protein sequence is unrelated to that of any known ion- transport-related protein. Selective solubilization studies using detergents show that while the protein is strongly associated with the phospholipid bilayer, it also binds to the cytoskeleton. The predicted polypeptide has a single trans-membranous hydrophobic segment near the N-terminus, which would locate it in the membrane; the large C-terminal domain is hydrophilic and cytoplasmic in orientation and is presumed to be responsible for the attachment to the cytoskeleton. By inference, the protein has the function of closing a latent ion channel. The messenger RNA encoding this protein is ubiquitously distributed in different human cell types and tissues and is thus presumably a widely distributed regulator of transmembrane cation fluxes. As a membrane- bound inhibitor protein of Na+ and K+ transport, it is unique among the known components of membrane-transport proteins.
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Stewart, GW, BE Hepworth-Jones, JN Keen, BC Dash, AC Argent, and CM Casimir. "Isolation of cDNA coding for an ubiquitous membrane protein deficient in high Na+, low K+ stomatocytic erythrocytes." Blood 79, no. 6 (March 15, 1992): 1593–601. http://dx.doi.org/10.1182/blood.v79.6.1593.bloodjournal7961593.
Full textAbstract:
Human red blood cells (RBCs) that are deficient in an integral membrane- associated protein (“stomatin“) of apparent molecular mass 31 Kd show a catastrophic increase in passive membrane permeability to the univalent cations Na+ and K+ and are stomatocytic in shape. We have purified this protein from normal RBC membranes and isolated a cDNA clone coding for it. The deduced protein sequence is unrelated to that of any known ion- transport-related protein. Selective solubilization studies using detergents show that while the protein is strongly associated with the phospholipid bilayer, it also binds to the cytoskeleton. The predicted polypeptide has a single trans-membranous hydrophobic segment near the N-terminus, which would locate it in the membrane; the large C-terminal domain is hydrophilic and cytoplasmic in orientation and is presumed to be responsible for the attachment to the cytoskeleton. By inference, the protein has the function of closing a latent ion channel. The messenger RNA encoding this protein is ubiquitously distributed in different human cell types and tissues and is thus presumably a widely distributed regulator of transmembrane cation fluxes. As a membrane- bound inhibitor protein of Na+ and K+ transport, it is unique among the known components of membrane-transport proteins.
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Blanchard, Maxime G., Jean-Philippe Longpré, Bernadette Wallendorff, and Jean-Yves Lapointe. "Measuring ion transport activities in Xenopus oocytes using the ion-trap technique." American Journal of Physiology-Cell Physiology 295, no. 5 (November 2008): C1464—C1472. http://dx.doi.org/10.1152/ajpcell.00560.2007.
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The ion-trap technique is an experimental approach allowing measurement of changes in ionic concentrations within a restricted space (the trap) comprised of a large-diameter ion-selective electrode apposed to a voltage-clamped Xenopus laevis oocyte. The technique is demonstrated with oocytes expressing the Na+/glucose cotransporter (SGLT1) using Na+- and H+-selective electrodes and with the electroneutral H+/monocarboxylate transporter (MCT1). In SGLT1-expressing oocytes, bath substrate diffused into the trap within 20 s, stimulating Na+/glucose influx, which generated a measurable decrease in the trap Na+ concentration ([Na+]T) by 0.080 ± 0.009 mM. Membrane hyperpolarization produced a further decrease in [Na+]T, which was proportional to the increased cotransport current. In a Na+-free, weakly buffered solution (pH 5.5), H+ drives glucose transport through SGLT1, and this was monitored with a H+-selective electrode. Proton movements can also be clearly detected on adding lactate to an oocyte expressing MCT1 (pH 6.5). For SGLT1, time-dependent changes in [Na+]T or [H+]T were also detected during a membrane potential pulse (150 ms) in the presence of substrate. In the absence of substrate, hyperpolarization triggered rapid reorientation of SGLT1 cation binding sites, accompanied by cation capture from the trap. The resulting change in [Na+]T or [H+]T is proportional to the pre-steady-state charge movement. The ion-trap technique can thus be used to measure steady-state and pre-steady-state transport activities and provides new opportunities for studying electrogenic and electroneutral ion transport mechanisms.
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GARG, RAVISH, VIJAY KUMAR, DINESH KUMAR, and S. K. CHAKARVARTI. "ELECTRICAL TRANSPORT THROUGH MICRO POROUS TRACK ETCH MEMBRANES OF SAME POROSITY." Modern Physics Letters B 26, no. 31 (November 2, 2012): 1250209. http://dx.doi.org/10.1142/s0217984912502090.
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Porosity, pore size and thickness of membrane are vital factors to influence the transport phenomena through micro porous track etch membranes (TEMs) and affect the various applications like separations, drug release, flow control, bio-sensing and cell size detection etc. based on transport process. Therefore, a better understanding of transport mechanism through TEMs is required for new applications in various thrust areas like biomedical devices and packaging of foods and drugs. Transport studies of electrolytic solutions of potassium chloride, through porous polycarbonate TEMS having cylindrical pores of size 0.2 μm and 0.4 μm with same porosity of 15%, have been carried out using an electrochemical cell. In this technique, the etched filter is sandwiched between two compartments of cell in such a way that the TEM acts as a membrane separating the cell into two chambers. The two chambers are then filled with electrolyte solution ( KCl in distilled water). The current voltage characteristics have been drawn by stepping the voltage ranging 0 to 10 V using Keithley 2400 Series Source Measurement Unit. The results indicate that rate of ion transport through cylindrical pores although is independent of pore size of TEMs of same porosity but there seems to be effect of TEM aperture size exposed to the electrolyte used in conducting cell on ion transport magnitude. From the experimental studies, a large deviation in the conduction through TEMs was observed when compared with theoretical consideration which led to the need for modification in the applicability of simple Ohm's law to the conduction through TEMs. It is found that ion transport increases with increase in area of aperture of TEM but much lower than the expected theoretically value.
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Altenberg, G. A., M. Subramanyam, and L. Reuss. "Muscarinic stimulation of gallbladder epithelium. II. Fluid transport, cell volume, and ion permeabilities." American Journal of Physiology-Cell Physiology 265, no. 6 (December 1, 1993): C1613—C1619. http://dx.doi.org/10.1152/ajpcell.1993.265.6.c1613.
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Activation of muscarinic receptors in the fluid-absorptive epithelium of the Necturus gallbladder elevates cytosolic Ca2+ concentration, transiently hyperpolarizes the cell membrane voltages, and decreases the apparent fractional resistance of the apical membrane [G. A. Altenberg, M. Subramanyam, J. S. Bergmann, K. M. Johnson, and L. Reuss. Am. J. Physiol. 265 (Cell Physiol. 34): C1604-C1612, 1993]. In these studies, we show that at the peak of the hyperpolarization both apical and basolateral membrane resistances (Ra and Rb, respectively) decreased, but in 2-3 min Ra returned to control values while Rb rose to a level approximately 60% higher than control. The acetylcholine (ACh)-induced decrease in Ra is caused by activation of apical membrane maxi K+ channels secondary to elevation of cytosolic Ca2+ concentration. The increase in Rb is due to decreases in K+ and Cl- conductances. ACh had no effects on cell KCl content or water volume, although K+ conductance transiently increased. These results can be explained by the changes in basolateral membrane conductances. ACh did not alter fluid absorption. In conclusion, ACh has complex time-dependent effects on K+ and Cl- electrodiffusive permeabilities without measurable changes in cell volume or in the rate of transepithelial fluid transport.
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Yu, Weiqun, Puneet Khandelwal, and Gerard Apodaca. "Distinct Apical and Basolateral Membrane Requirements for Stretch-induced Membrane Traffic at the Apical Surface of Bladder Umbrella Cells." Molecular Biology of the Cell 20, no. 1 (January 2009): 282–95. http://dx.doi.org/10.1091/mbc.e08-04-0439.
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Epithelial cells respond to mechanical stimuli by increasing exocytosis, endocytosis, and ion transport, but how these processes are initiated and coordinated and the mechanotransduction pathways involved are not well understood. We observed that in response to a dynamic mechanical environment, increased apical membrane tension, but not pressure, stimulated apical membrane exocytosis and ion transport in bladder umbrella cells. The exocytic response was independent of temperature but required the cytoskeleton and the activity of a nonselective cation channel and the epithelial sodium channel. The subsequent increase in basolateral membrane tension had the opposite effect and triggered the compensatory endocytosis of added apical membrane, which was modulated by opening of basolateral K+ channels. Our results indicate that during the dynamic processes of bladder filling and voiding apical membrane dynamics depend on sequential and coordinated mechanotransduction events at both membrane domains of the umbrella cell.
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Bjerregaard, Henning F. "Side-specific Toxic Effects on the Membranes of Cultured Renal Epithelial Cells (A6)." Alternatives to Laboratory Animals 23, no. 4 (July 1995): 485–90. http://dx.doi.org/10.1177/026119299502300411.
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- A cultured epithelial cell line from toad kidney (A6) was used to investigate side-specific toxicity related to the apical (outer) and basolateral (inner) membranes of epithdia. Well-known inhibitors and stimulators of ion transport were used to show that the ion transport proteins are asymmetrically distributed: the apical membrane contains sodium and chloride channels and the basolateral membrane contains Na+/K+ pumps, Na+/Cl- co-transporters, potassium channels and receptors for antidiuretic hormone The data demonstrate that the cellular toxicity of chemicals decreases when they are added to the apical side, illustrating that the epithelium acts as a functional barrier. However, the side-specific toxicity was more pronounced for ions and water-soluble molecules than for organic solvents, indicating that A6 epitheha can be used to distinguish between drugs that target specific membrane proteins and those that target membrane lipids. Furthermore, the cell line could be used to pick up chemicals that, at low concentrations inhibit sodium absorption and chloride secretion, without having any effect on cellular toxicity.
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Diaz, Maira, Maria Jose Sanchez-Barrena, Juana Maria Gonzalez-Rubio, Lesia Rodriguez, Daniel Fernandez, Regina Antoni, Cristina Yunta, et al. "Calcium-dependent oligomerization of CAR proteins at cell membrane modulates ABA signaling." Proceedings of the National Academy of Sciences 113, no. 3 (December 30, 2015): E396—E405. http://dx.doi.org/10.1073/pnas.1512779113.
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Regulation of ion transport in plants is essential for cell function. Abiotic stress unbalances cell ion homeostasis, and plants tend to readjust it, regulating membrane transporters and channels. The plant hormone abscisic acid (ABA) and the second messenger Ca2+ are central in such processes, as they are involved in the regulation of protein kinases and phosphatases that control ion transport activity in response to environmental stimuli. The identification and characterization of the molecular mechanisms underlying the effect of ABA and Ca2+ signaling pathways on membrane function are central and could provide opportunities for crop improvement. The C2-domain ABA-related (CAR) family of small proteins is involved in the Ca2+-dependent recruitment of the pyrabactin resistance 1/PYR1-like (PYR/PYL) ABA receptors to the membrane. However, to fully understand CAR function, it is necessary to define a molecular mechanism that integrates Ca2+ sensing, membrane interaction, and the recognition of the PYR/PYL interacting partners. We present structural and biochemical data showing that CARs are peripheral membrane proteins that functionally cluster on the membrane and generate strong positive membrane curvature in a Ca2+-dependent manner. These features represent a mechanism for the generation, stabilization, and/or specific recognition of membrane discontinuities. Such structures may act as signaling platforms involved in the recruitment of PYR/PYL receptors and other signaling components involved in cell responses to stress.
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Lamprecht, G., U. Seidler, and M. Classen. "Intracellular pH-regulating ion transport mechanisms in parietal cell basolateral membrane vesicles." American Journal of Physiology-Gastrointestinal and Liver Physiology 265, no. 5 (November 1, 1993): G903—G910. http://dx.doi.org/10.1152/ajpgi.1993.265.5.g903.
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Na(+)-H+ and Cl(-)-base exchangers on the parietal cell have been demonstrated by several authors. Controversy exists concerning a basolateral Na(+)-HCO3- cotransporter in the parietal cell. To clarify this issue, we prepared highly enriched basolateral membrane (BLM) and apical-tubulovesicular membrane (to serve as negative controls) vesicles from rabbit fundic mucosa. Na(+)-H+ exchange was demonstrated by measuring pH gradient-driven amiloride-sensitive 22Na+ uptake and Na+ gradient-driven proton uptake into voltage-clamped BLM but not into apical-tubulovesicular vesicles. Anion exchange was demonstrated by measuring 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS)-inhibitable influx of 36Cl- into Cl(-)- or HCO3(-)-loaded voltage-clamped BLM vesicles. Na(+)-HCO3- cotransport was assessed by comparing HCO3(-)-driven 22Na uptake with uptake driven by an identical pH gradient. No significant difference was found between 22Na uptake in the presence and absence of HCO3-; 1 mM amiloride inhibited 22Na uptake > 90% in both conditions, whereas 2 mM DIDS had no effect. In BLM vesicles prepared from rabbit renal cortex, however, a HCO3- gradient stimulated 22Na uptake much more than an equivalent pH gradient, and DIDS inhibited this HCO3- gradient-driven 22Na uptake. This indicates that our experimental setup was suitable to detect a Na(+)-HCO3- cotransporter if present. Our data suggest that the parietal cell BLM contains Na(+)-H+ exchangers and Cl(-)-HCO3- exchangers but no Na(+)-HCO3- cotransporter.
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Middleton, J. P., A. W. Mangel, S. Basavappa, and J. G. Fitz. "Nucleotide receptors regulate membrane ion transport in renal epithelial cells." American Journal of Physiology-Renal Physiology 264, no. 5 (May 1, 1993): F867—F873. http://dx.doi.org/10.1152/ajprenal.1993.264.5.f867.
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Regulation of plasma membrane ion transport by endogenous purinergic receptors was assessed in a distal renal (A6) cell line. Nucleotide analogues stimulated Na-K-Cl cotransport activity with relative potencies of ATP > UTP > ATP gamma S > 2-methylthio-ATP = alpha,beta-methylene ATP. Activation of nucleotide receptors with extracellular ATP and nucleotide analogues increased intracellular calcium concentration ([Ca2+]i) primarily by release of intracellular calcium stores, with relative potency of agonists similar to that seen for stimulation of Na-K-Cl cotransport. Neither the change in [Ca2+]i nor the stimulation of cotransport was abolished by the adenosine receptor antagonist 8-(4-[N-(2-aminoethyl)carbamoylmethoxy]-phenyl)-1,3-dipropylxanthi ne (XAC). In contrast to the adenosine A2 receptor agonist 5'-N-ethylcarboxamidoadenosine, nucleotide analogues had no discernible effect on cytosolic adenosine 3',5'-cyclic monophosphate levels or adenylyl cyclase activity. To address possible mechanisms for stimulation of Na-K-Cl cotransport by the nucleotide receptor, 125I efflux and patch-clamp studies were used to measure chloride secretion. ATP and ionomycin markedly enhanced 125I efflux and whole cell currents, consistent with activation of chloride conductance pathways. Diphenylamine-2-carboxylate, a chloride channel blocker, eliminated the effects of ionomycin, forskolin, adenosine, and ATP on Na-K-Cl cotransport. This study demonstrates that nucleotide receptors in this model of renal epithelium initiate distinct regulation of Na-K-Cl cotransport. Nucleotide receptors may effect their responses through primary activation of membrane chloride channels.
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Fernández de Labastida, Marc, and Andriy Yaroshchuk. "Nanofiltration of Multi-Ion Solutions: Quantitative Control of Concentration Polarization and Interpretation by Solution-Diffusion-Electro-Migration Model." Membranes 11, no. 4 (April 8, 2021): 272. http://dx.doi.org/10.3390/membranes11040272.
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For effective use of advanced engineering models of nanofiltration quality of experimental input is crucial, especially in electrolyte mixtures where simultaneous rejections of various ions may be very different. In particular, this concerns the quantitative control of concentration polarization (CP). This work used a rotating disklike membrane test cell with equally accessible membrane surface, so the CP extent was the same over the membrane surface. This condition, which is not satisfied in the conventional membrane test cell, made possible correcting for CP easily even in multi-ion systems. Ion rejections were studied experimentally for several dominant salts (NaCl, MgCl2, Na2SO4 and MgSO4) and trace ions (Na+, NH4+, Cl− and NO3−) using NF270 membrane. The solution–diffusion–electro–migration model was used to obtain ion permeances from the experimental measurements. The model could well fit the experimental data except in the case of NH4+. The correlations between the ion permeances and type of dominant salt are discussed in the context of the established mechanisms of NF such as Donnan and dielectric exclusion. The obtained information contributes to the systematic transport characterization of NF membranes and may be ultimately useful for computational fluid dynamics simulations of the performance of the membranes in various applications.
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Garvin, J. L., and K. R. Spring. "Regulation of apical membrane ion transport in Necturus gallbladder." American Journal of Physiology-Cell Physiology 263, no. 1 (July 1, 1992): C187—C193. http://dx.doi.org/10.1152/ajpcell.1992.263.1.c187.
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Na and Cl movement through the apical membrane of Necturus gallbladder epithelium was investigated using electrophysiological and light microscopic measurements. Changes in membrane potential difference, fractional resistance of the apical membrane, and transepithelial resistance caused by changes in apical bath Cl concentration revealed the presence of a Cl conductance in the apical membrane of control tissues that was apparently not present in the preparations studied by other investigators. This Cl conductance was blocked by bumetanide (10(-5) M) or by the inhibitor of adenosine 3',5'-cyclic monophosphate (cAMP) action, the Rp isomer of adenosine 3',5'-cyclic monophosphorothioate (Rp-cAMPS; 0.5 mM). Treatment of the tissues with Rp-cAMPS also eliminated bumetanide-sensitive cell swelling in the presence of ouabain and activated an amiloride-sensitive swelling, changes consistent with inhibition of NaCl cotransport and the activation of Na-H and Cl-HCO3 exchange. We conclude that the mode of NaCl entry into Necturus gallbladder epithelial cells is determined by the level of cAMP. When cAMP levels are high, entry occurs by NaCl cotransport; when cAMP levels are low, parallel exchange of Na-H and Cl-HCO3 predominates. These observations explain the previous disagreements about the mode of NaCl entry into Necturus gallbladder epithelial cells.
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Calahorra, Martha, Jorge Ramírez, S. Mónica Clemente, and Antonio Peña. "Electrochemical potential and ion transport in vesicles of yeast plasma membrane." Biochimica et Biophysica Acta (BBA) - Biomembranes 899, no. 2 (May 1987): 229–38. http://dx.doi.org/10.1016/0005-2736(87)90404-4.
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Chen, Tsung-Yu, and Tzyh-Chang Hwang. "CLC-0 and CFTR: Chloride Channels Evolved From Transporters." Physiological Reviews 88, no. 2 (April 2008): 351–87. http://dx.doi.org/10.1152/physrev.00058.2006.
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CLC-0 and cystic fibrosis transmembrane conductance regulator (CFTR) Cl− channels play important roles in Cl− transport across cell membranes. These two proteins belong to, respectively, the CLC and ABC transport protein families whose members encompass both ion channels and transporters. Defective function of members in these two protein families causes various hereditary human diseases. Ion channels and transporters were traditionally viewed as distinct entities in membrane transport physiology, but recent discoveries have blurred the line between these two classes of membrane transport proteins. CLC-0 and CFTR can be considered operationally as ligand-gated channels, though binding of the activating ligands appears to be coupled to an irreversible gating cycle driven by an input of free energy. High-resolution crystallographic structures of bacterial CLC proteins and ABC transporters have led us to a better understanding of the gating properties for CLC and CFTR Cl− channels. Furthermore, the joined force between structural and functional studies of these two protein families has offered a unique opportunity to peek into the evolutionary link between ion channels and transporters. A promising byproduct of this exercise is a deeper mechanistic insight into how different transport proteins work at a fundamental level.
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Stetson, D. L. "Turtle urinary bladder: regulation of ion transport by dynamic changes in plasma membrane area." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 257, no. 5 (November 1, 1989): R973—R981. http://dx.doi.org/10.1152/ajpregu.1989.257.5.r973.
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Turtle urinary bladder possesses four ion transport processes: Na+ absorption, H+ secretion, and HCO3- secretion-Cl- absorption. Each transport process is performed by a specific epithelial cell type. Granular cells absorb Na+ but they are not sensitive to antidiuretic hormone (ADH), unlike toad bladder granular cells. alpha-Carbonic anhydrase-rich (CA) cells secrete H+ via an apical H+-adenosinetriphosphatase (ATPase). Under conditions of low CO2 tension, this active pump is contained in the limiting membranes of certain cytoplasmic vesicles. The vesicles fuse with the apical membrane, and H+ pumps are incorporated into that membrane, as physiological conditions demand increased H+ secretion. The stimulus for fusion of these vesicles with the apical membrane appears to be intracellular acidification. beta-CA cells secrete HCO3- and reabsorb Cl-, both processes driven by H+-ATPase in the basolateral membrane in series with an apical Cl- -HCO3- exchanger. Increased intracellular adenosine 3',5'-cyclic monophosphate concentration in beta-cells stimulates net HCO3- secretion and induces an electrogenic component of this flux by activating an apical Cl- channel. This activation accompanies the fusion of an intracellular tubulovesicular network with the apical membrane. The membrane of this network may contain Cl- channels.
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Wang, Xuan, Peng An, Zhenglong Gu, Yongting Luo, and Junjie Luo. "Mitochondrial Metal Ion Transport in Cell Metabolism and Disease." International Journal of Molecular Sciences 22, no. 14 (July 14, 2021): 7525. http://dx.doi.org/10.3390/ijms22147525.
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Mitochondria are vital to life and provide biological energy for other organelles and cell physiological processes. On the mitochondrial double layer membrane, there are a variety of channels and transporters to transport different metal ions, such as Ca2+, K+, Na+, Mg2+, Zn2+ and Fe2+/Fe3+. Emerging evidence in recent years has shown that the metal ion transport is essential for mitochondrial function and cellular metabolism, including oxidative phosphorylation (OXPHOS), ATP production, mitochondrial integrity, mitochondrial volume, enzyme activity, signal transduction, proliferation and apoptosis. The homeostasis of mitochondrial metal ions plays an important role in maintaining mitochondria and cell functions and regulating multiple diseases. In particular, channels and transporters for transporting mitochondrial metal ions are very critical, which can be used as potential targets to treat neurodegeneration, cardiovascular diseases, cancer, diabetes and other metabolic diseases. This review summarizes the current research on several types of mitochondrial metal ion channels/transporters and their functions in cell metabolism and diseases, providing strong evidence and therapeutic strategies for further insights into related diseases.
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Naranjo, David, Hans Moldenhauer, Matías Pincuntureo, and Ignacio Díaz-Franulic. "Pore size matters for potassium channel conductance." Journal of General Physiology 148, no. 4 (September 12, 2016): 277–91. http://dx.doi.org/10.1085/jgp.201611625.
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Ion channels are membrane proteins that mediate efficient ion transport across the hydrophobic core of cell membranes, an unlikely process in their absence. K+ channels discriminate K+ over cations with similar radii with extraordinary selectivity and display a wide diversity of ion transport rates, covering differences of two orders of magnitude in unitary conductance. The pore domains of large- and small-conductance K+ channels share a general architectural design comprising a conserved narrow selectivity filter, which forms intimate interactions with permeant ions, flanked by two wider vestibules toward the internal and external openings. In large-conductance K+ channels, the inner vestibule is wide, whereas in small-conductance channels it is narrow. Here we raise the idea that the physical dimensions of the hydrophobic internal vestibule limit ion transport in K+ channels, accounting for their diversity in unitary conductance.
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Briskin, Donald P. "Plasma membrane H+-transporting ATPase: Role in potassium ion transport?" Physiologia Plantarum 68, no. 1 (September 1986): 159–63. http://dx.doi.org/10.1111/j.1399-3054.1986.tb06612.x.
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Schwab, Albrecht, and Christian Stock. "Ion channels and transporters in tumour cell migration and invasion." Philosophical Transactions of the Royal Society B: Biological Sciences 369, no. 1638 (March 19, 2014): 20130102. http://dx.doi.org/10.1098/rstb.2013.0102.
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Cell migration is a central component of the metastatic cascade requiring a concerted action of ion channels and transporters (migration-associated transportome), cytoskeletal elements and signalling cascades. Ion transport proteins and aquaporins contribute to tumour cell migration and invasion among other things by inducing local volume changes and/or by modulating Ca 2+ and H + signalling. Targeting cell migration therapeutically bears great clinical potential, because it is a prerequisite for metastasis. Ion transport proteins appear to be attractive candidate target proteins for this purpose because they are easily accessible as membrane proteins and often overexpressed or activated in cancer. Importantly, a number of clinically widely used drugs are available whose anticipated efficacy as anti-tumour drugs, however, has now only begun to be evaluated.
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Hunter, M., J. D. Horisberger, B. Stanton, and G. Giebisch. "The collecting tubule of Amphiuma. I. Electrophysiological characterization." American Journal of Physiology-Renal Physiology 253, no. 6 (December 1, 1987): F1263—F1272. http://dx.doi.org/10.1152/ajprenal.1987.253.6.f1263.
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Single collecting tubules of Amphiuma kidneys were perfused in vitro to characterize their electrophysiological properties. The lumen-negative potential (-24 mV) was abolished by amiloride in the lumen and by ouabain in the bath. Ion substitution experiments in the lumen demonstrated the presence of a large sodium conductance in the apical cell membrane, but no evidence was obtained for a significant potassium or chloride conductance. Ion substitutions in the bath solution and the depolarizing effect of barium on the basolateral membrane potential demonstrated the presence of a large potassium conductance in the basolateral cell membrane. Measurements of dilution potentials in amiloride-treated tubules revealed a modest cation selectivity of the paracellular pathway. These results support a cell model in which sodium reabsorption occurs by electrodiffusion across the apical cell membrane and active transport across the basolateral cell membrane. The absence of a detectable potassium conductance in the apical cell membrane suggests that secretion of this ion cannot take place by diffusion from cell to lumen.
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LANG, FLORIAN, GILLIAN L. BUSCH, MARKUS RITTER, HARALD VÖLKL, SIEGFRIED WALDEGGER, ERICH GULBINS, and DIETER HÄUSSINGER. "Functional Significance of Cell Volume Regulatory Mechanisms." Physiological Reviews 78, no. 1 (January 1, 1998): 247–306. http://dx.doi.org/10.1152/physrev.1998.78.1.247.
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Lang, Florian, Gillian L. Busch, Markus Ritter, Harald Völkl, Siegfried Waldegger, Erich Gulbins, and Dieter Häussinger. Functional Significance of Cell Volume Regulatory Mechanisms. Physiol. Rev. 78: 247–306, 1998. — To survive, cells have to avoid excessive alterations of cell volume that jeopardize structural integrity and constancy of intracellular milieu. The function of cellular proteins seems specifically sensitive to dilution and concentration, determining the extent of macromolecular crowding. Even at constant extracellular osmolarity, volume constancy of any mammalian cell is permanently challenged by transport of osmotically active substances across the cell membrane and formation or disappearance of cellular osmolarity by metabolism. Thus cell volume constancy requires the continued operation of cell volume regulatory mechanisms, including ion transport across the cell membrane as well as accumulation or disposal of organic osmolytes and metabolites. The various cell volume regulatory mechanisms are triggered by a multitude of intracellular signaling events including alterations of cell membrane potential and of intracellular ion composition, various second messenger cascades, phosphorylation of diverse target proteins, and altered gene expression. Hormones and mediators have been shown to exploit the volume regulatory machinery to exert their effects. Thus cell volume may be considered a second message in the transmission of hormonal signals. Accordingly, alterations of cell volume and volume regulatory mechanisms participate in a wide variety of cellular functions including epithelial transport, metabolism, excitation, hormone release, migration, cell proliferation, and cell death.
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Candia, O. A., L. R. Grillone, and T. C. Chu. "Forskolin effects on frog and rabbit corneal epithelium ion transport." American Journal of Physiology-Cell Physiology 251, no. 3 (September 1, 1986): C448—C454. http://dx.doi.org/10.1152/ajpcell.1986.251.3.c448.
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The effects of forskolin on the electrophysiological parameters of the isolated corneal epithelium from bullfrog (Rana catesbeiana) were investigated. Forskolin stimulated the short-circuit current (SCC) and transepithelial potential difference (PDt), while reducing the transepithelial resistance. These effects were absent in Cl- -free bathing solutions. Furosemide, added either before or after forskolin, completely blocked the effects. Epinephrine and A23187, added after forskolin, produced only a small additional stimulation of the SCC. Propranolol neither blocked nor reduced the effect of forskolin. Forskolin increased the stroma to tear 36Cl flux by 61% and the tear to stroma 36Cl flux by 64%. Intracellular recordings showed that forskolin depolarized the potential difference across the apical membrane and reduced the apical/basolateral resistance ratio. Intracellular recordings in the isolated rabbit epithelium showed the same effects by forskolin except that there was only a brief stimulation of PDt, after which it stabilized slightly below the control level. These results are consistent with an increase in apical membrane permeability similar to that produced by adenosine 3',5'-cyclic monophosphate, epinephrine, and the Ca2+ ionophore A23187.
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Forney, L. J. "Gas diffusion electrode-membrane cells: effects of ion transport." Industrial & Engineering Chemistry Research 32, no. 6 (June 1993): 1204–11. http://dx.doi.org/10.1021/ie00018a028.
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Zhou, Xianfeng, Punam Dalai, and Nita Sahai. "Semipermeable Mixed Phospholipid-Fatty Acid Membranes Exhibit K+/Na+ Selectivity in the Absence of Proteins." Life 10, no. 4 (April 14, 2020): 39. http://dx.doi.org/10.3390/life10040039.
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Two important ions, K+ and Na+, are unequally distributed across the contemporary phospholipid-based cell membrane because modern cells evolved a series of sophisticated protein channels and pumps to maintain ion gradients. The earliest life-like entities or protocells did not possess either ion-tight membranes or ion pumps, which would result in the equilibration of the intra-protocellular K+/Na+ ratio with that in the external environment. Here, we show that the most primitive protocell membranes composed of fatty acids, that were initially leaky, would eventually become less ion permeable as their membranes evolved towards having increasing phospholipid contents. Furthermore, these mixed fatty acid-phospholipid membranes selectively retain K+ but allow the passage of Na+ out of the cell. The K+/Na+ selectivity of these mixed fatty acid-phospholipid semipermeable membranes suggests that protocells at intermediate stages of evolution could have acquired electrochemical K+/Na+ ion gradients in the absence of any macromolecular transport machinery or pumps, thus potentially facilitating rudimentary protometabolism.