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Ben-Dov N, Korenstein R. Proton-induced endocytosis is dependent on cell membrane fluidity, lipid-phase order and the membrane resting potential. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1828:2672-81. [PMID: 23911577 DOI: 10.1016/j.bbamem.2013.07.027] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/28/2013] [Revised: 07/20/2013] [Accepted: 07/22/2013] [Indexed: 01/13/2023]
Abstract
Recently it has been shown that decreasing the extracellular pH of cells stimulates the formation of inward membrane invaginations and vesicles, accompanied by an enhanced uptake of macromolecules. This type of endocytosis was coined as proton-induced uptake (PIU). Though the initial induction of inward membrane curvature was rationalized in terms of proton-based increase of charge asymmetry across the membrane, the dependence of the phenomenon on plasma membrane characteristics is still unknown. The present study shows that depolarization of the membrane resting potential elevates PIU by 25%, while hyperpolarization attenuates it by 25%. Comparison of uptake in suspended and adherent cells implicates that the resting-potential affects PIU through remodeling the actin-cytoskeleton. The pH at the external interface of the cell membrane rather than the pH gradient across it determines the extent of PIU. PIU increases linearly upon temperature increase in the range of 4-36°C, in correlation with the membrane fluidity. The plasma membrane fluidity and the lipid phase order are modulated by enriching the cell's membrane with cholesterol, tergitol, dimethylsulfoxide, 6-ketocholestanol and phloretin and by cholesterol depletion. These treatments are shown to alter the extent of PIU and are better correlated with membrane fluidity than with the lipid phase order. We suggest that the lipid phase order and fluidity influence PIU by regulating the lipid order gradient across the perimeter of the lipid-condensed microdomains (rafts) and alter the characteristic tension line that separates the higher ordered lipid-domains from the lesser ordered ones.
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Affiliation(s)
- Nadav Ben-Dov
- Department of Physiology and Pharmacology, Faculty of Medicine, Tel-Aviv University, 69978 Tel-Aviv, Israel.
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McNamara JC, Faria SC. Evolution of osmoregulatory patterns and gill ion transport mechanisms in the decapod Crustacea: a review. J Comp Physiol B 2012; 182:997-1014. [DOI: 10.1007/s00360-012-0665-8] [Citation(s) in RCA: 120] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2011] [Revised: 04/02/2012] [Accepted: 04/04/2012] [Indexed: 10/28/2022]
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3
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Demmers KJ, Carter D, Fan S, Mao P, Maqbool NJ, McLeod BJ, Bartolo R, Butt AG. Molecular and functional characterization of the cystic fibrosis transmembrane conductance regulator from the Australian common brushtail possum, Trichosurus vulpecula. J Comp Physiol B 2009; 180:545-61. [PMID: 20012660 DOI: 10.1007/s00360-009-0433-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2009] [Revised: 11/14/2009] [Accepted: 11/19/2009] [Indexed: 02/07/2023]
Abstract
Unlike eutherian mammals, the colon of the Australian common brushtail possum, Trichosurus vulpecula, a metatherian mammal, is incapable of electrogenic Cl(-) secretion and has elevated levels of electrogenic Na(+) absorption, while the ileum secretes HCO (3) (-) rather than Cl(-). In eutherian mammals, the cystic fibrosis transmembrane conductance regulator (CFTR) is essential for both Cl(-) and HCO (3) (-) secretion and the regulation of Na(+) absorption. Therefore, we have sequenced possum (p)CFTR, described its distribution and characterized the properties of cloned pCFTR expressed in Fischer rat thyroid (FRT) cells. pCFTR (GenBank accession No. AY916796) has a 1,478 amino acid open reading frame, which has >90% identity with CFTR from other marsupials and >80% identity with non-rodent eutherian mammals. In pCFTR, there is a high level of conservation of the transmembrane and nucleotide binding domains although, with the exception of other marsupials, there is considerable divergence from other species in the R domain. FRT cells transfected with pCFTR express mature CFTR protein which functions as a small Cl(-) channel activated by cAMP-dependent phosphorylation. In whole-cell recordings it has a linear, time and voltage-independent conductance, with a selectivity sequence P(Br) > P(Cl) > P(I) > P(HCO)(3) >> P(Gluconate). pCFTR transcript is present in a range of epithelia, including the ileum and the colon. The presence of pCFTR in the ileum and its measured HCO (3) (-) permeability suggest that it may be involved in ileal HCO (3) (-) secretion. Why the possum colon does not secrete Cl(-) and has elevated electrogenic Na(+) absorption, despite the apparent expression of CFTR, remains to be determined.
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Affiliation(s)
- K J Demmers
- AgResearch, Invermay Agricultural Centre, Private Bag 50034, Mosgiel 9024, New Zealand
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Bartolo RC, Harfoot N, Gill M, Demmers K, McLeod B, Butt AG. Electrogenic Cl(-) secretion does not occur in the ileum of the Australian common brushtail possum, Trichosurus vulpecula, due to low levels of expression of the NaK2Cl cotransporter, NKCC1. J Comp Physiol B 2009; 179:997-1010. [PMID: 19565248 DOI: 10.1007/s00360-009-0379-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2009] [Revised: 06/05/2009] [Accepted: 06/12/2009] [Indexed: 11/25/2022]
Abstract
The colon of the brushtail possum does not have an electrogenic secretory response. Given the functional significance of electrogenic Cl(-) secretion in the intestine of eutherian mammals, we have investigated the secretory response in the small intestine of this marsupial. In the Ussing chamber cAMP-dependent secretagogues stimulated a sustained increase in ileal short-circuit current (Isc), whereas Ca(2+)-dependent secretagogues induced a transient increase. Both the responses were inhibited by mucosal addition of the anion channel blocker 5-nitro-2-(3-phenylpropylamino) benzoic acid (100 mciromol l(-1)), consistent with an anion secretory response. However, the responses were not inhibited by serosal bumetanide (10 mciromol l(-1)) and were independent of bath Cl(-), indicating that the stimulated ileal Isc does not involve electrogenic Cl(-) secretion driven by the NaK2Cl cotransporter, NKCC1. Consistent with this, there were low levels of NKCC1 expression in the ileal epithelium. In particular, NKCC1 expression in the ileal crypt cells was comparable to that of the villous cells. This differs from eutherian mammals where high levels of NKCC1 expression in the ileal crypt cells are associated with their role in Cl(-) secretion. The cAMP- and Ca(2+)-dependent secretory responses were inhibited by the removal of HCO(3) (-) suggesting that these responses were due to electrogenic HCO(3) (-) secretion. We conclude that the ileum of the possum does not secrete Cl(-) due to low levels of NKCC1 expression. It does however appear to secrete HCO(3) (-). These results are further significant examples of differences in the transport function of the possum intestinal epithelium compared with eutherian mammals.
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Affiliation(s)
- Ray C Bartolo
- Invermay Agricultural Centre, AgResearch, Private Bag 50034, Mosgiel, 9024, New Zealand
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Butler DG, Lam W, Tong J. ANG II-induced attenuation of duck salt gland secretion does not depend upon the release of adrenal catecholamines. J Comp Physiol B 2005; 176:35-43. [PMID: 16292650 DOI: 10.1007/s00360-005-0029-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2005] [Revised: 08/05/2005] [Accepted: 08/24/2005] [Indexed: 10/25/2022]
Abstract
Pekin ducks (Anas platyrhynchos) were bilaterally adrenalectomized (ADX) using a two-stage procedure and given daily i.m. injections of 1 mg kg bw(-1) of dexamethasone (DEXA), a steroid lacking mineralocorticoid activity, and 0.9% saline drinking water ad libitum to counterbalance renal losses of salt and water. Mean arterial blood pressure (mmHg) fell from 161+/- 3.7 (intact controls) to 116 +/- 6.9 (bilateral ADX+DEXA), a decrease of 27%, but heart rates (HR) were unchanged. The nasal salt glands were fully active after ADX + DEXA. Rates of fluid secretion and electrolyte and osmolal concentrations were unchanged. Secretion stopped, then rebounded several minutes later if ADX + DEXA ducks were injected i.v. with 1 microg of [Asn(1),Val(5)]-angiotensin II (ANG II) kg bw(-1) which showed that attenuation was not adrenal catecholamine-dependent.
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Lyall P, Armstrong WM, Lyall V. Effect of HCO(3)(-) on TPA- and IBMX-induced anion conductances in Necturus gallbladder epithelial cells. Am J Physiol Cell Physiol 2000; 279:C1385-92. [PMID: 11029286 DOI: 10.1152/ajpcell.2000.279.5.c1385] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Effects of HCO(3)(-) on protein kinase C (PKC)- and protein kinase A (PKA)-induced anion conductances were investigated in Necturus gallbladder epithelial cells. In HCO(3)(-)-free media, activation of PKC via 12-O-tetradecanoylphorbol 13-acetate (TPA) depolarized apical membrane potential (V(a)) and decreased fractional apical voltage ratio (F(R)). These effects were blocked by mucosal 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB), a Cl(-) channel blocker. In HCO(3)(-) media, TPA induced significantly greater changes in V(a) and F(R). These effects were blocked only when NPPB was present in both mucosal and basolateral compartments. The data suggest that TPA activates NPPB-sensitive apical Cl(-) conductance (g(Cl)(a)) in the absence of HCO(3)(-); in its presence, TPA stimulated both NPPB-sensitive g(Cl)(a) and basolateral Cl(-) conductance (g(Cl)(b)). Activation of PKA via 3-isobutyl-1-methylxanthine (IBMX) also decreased V(a) and F(R); however, these changes were not affected by external HCO(3)(-). We conclude that HCO(3)(-) modulates the effects of PKC on g(Cl)(b). In HCO(3)(-) medium, TPA and IBMX also induced an initial transient hyperpolarization and increase in intracellular pH. Because these changes were independent of mucosal Na(+) and Cl(-), it is suggested that TPA and IBMX induce a transient increase in apical HCO(3)(-) conductance.
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Affiliation(s)
- P Lyall
- Department of Physiology and Biophysics, Indiana University School of Medicine, Indianapolis, Indiana 46202-5102, USA
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7
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Retinal pigment epithelial transport mechanisms and their contributions to the electroretinogram. Prog Retin Eye Res 1997. [DOI: 10.1016/s1350-9462(96)00037-7] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Khalbuss WE, Marousis CG, Subramanyam M, Orlando RC. Effect of HCl on transmembrane potentials and intracellular pH in rabbit esophageal epithelium. Gastroenterology 1995; 108:662-72. [PMID: 7875468 DOI: 10.1016/0016-5085(95)90437-9] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
BACKGROUND/AIMS Acidification of the basolateral membrane by adding HCl to the serosal solution of esophageal epithelium leads to more necrosis than acidification of the apical membrane by adding HCl to the luminal solution. The aim of this study was to examine the mechanism for this difference. METHODS The effect of low extracellular pH (pHo) (HCl) on intracellular pH (pHi) and transmembrane potentials was examined in rabbit esophageal cells by impalement with intracellular microelectrodes. RESULTS Lowering luminal pH to 3.0 had no effect on membrane voltage and/or pHi in either luminally or serosally impaled cells, although a decline in both parameters occurred at pH 1.5 in luminally impaled cells. In contrast, lowering serosal pH from 7.4 to 3.0 progressively reduced membrane voltage and/or pHi. Membrane depolarization at low pHo was inhibited by a high-potassium solution or barium and mimicked by lowering pHi (gassing with CO2) at neutral pHo. CONCLUSIONS Basolateral, but not apical, membranes of esophageal epithelial cells are highly permeable to H+, accounting for the greater susceptibility to damage from exposure to serosal than luminal acid. Membrane depolarization at low pHo is mediated by low pHi through inhibition of basolateral membrane K+ conductance.
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Affiliation(s)
- W E Khalbuss
- Department of Medicine, Tulane University School of Medicine, New Orleans, Louisiana
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Shuttleworth TJ. Intracellular Signals Controlling Ionic and Acid-Base Regulation in Avian Nasal Gland Cells. ACTA ACUST UNITED AC 1995. [DOI: 10.1007/978-3-642-52363-2_8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/15/2023]
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10
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Abstract
In current models describing agonist-induced oscillations in [Ca2+]i, Ca2+ entry is generally assumed to have a simple sustaining role, replenishing Ca2+ lost from the cell and recharging intracellular Ca2+ stores. In cells from the avian nasal gland, a model exocrine cell, we show that inhibition of Ca2+ entry by La3+, SK&F 96365, or by membrane depolarization, rapidly blocks [Ca2+]i oscillations but does so without detectable depletion of agonist-sensitive Ca2+ stores. As the rate of Mn2+ quenching during [Ca2+]i oscillations is constant, Ca2+ entry is not directly contributing to the [Ca2+]i changes and, instead, appears to be involved in inducing the repetitive release of Ca2+ from internal stores. Together, these data contradict current models in that (i) at the low agonist concentrations where [Ca2+]i oscillations are seen, generated levels of Ins(1,4,5)P3 are themselves inadequate to result in a regenerative [Ca2+]i signal, and (ii) Ca2+ entry is necessary to actually drive the intrinsic oscillatory mechanism.
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Affiliation(s)
- S C Martin
- Department of Physiology, University of Rochester School of Medicine and Dentistry, NY 14642
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Charney AN, Kohlbrecher A, Pelkonen AM. NaCl flux in the flounder (Pseudopleuronectes americanus) intestine: effects of pH and transport inhibitors. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. COMPARATIVE PHYSIOLOGY 1993; 106:671-6. [PMID: 7906625 DOI: 10.1016/0300-9629(93)90379-i] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
1. The effects of extracellular pH on Na+ and Cl- absorption were studied in vitro in the small intestine of the winter flounder, Pseudopleuronectes americanus. 2. Reductions in bathing solution pH inhibited JNams (mucosal-to-serosal flux) and JNanet (net flux) (r = 0.90) and JClnet (r = 0.92) [due to an increase in JClsm (serosal-to-mucosal)] and decreased short circuit current (Isc). 3. Luminal bumetanide (0.1 mM) and amiloride (1 mM) inhibited Na+ and Cl- absorption by reducing Jms. 4. Luminal barium (5 mM) and luminal copper (100 microM) decreased JClms and increased JClsm. 5. We conclude that reductions in extracellular pH inhibit a luminal membrane NaCl absorptive process (Na(+)-K(+)-2Cl-) and stimulate an electrogenic Cl- secretory process.
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Affiliation(s)
- A N Charney
- Mount Desert Island Biological Laboratory, Salsbury Cove, ME 04672
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Torchia J, Lytle C, Pon D, Forbush B, Sen A. The Na-K-Cl cotransporter of avian salt gland. Phosphorylation in response to cAMP-dependent and calcium-dependent secretogogues. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(19)74061-7] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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13
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Zeuthen T. From contractile vacuole to leaky epithelia. Coupling between salt and water fluxes in biological membranes. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1113:229-58. [PMID: 1510998 DOI: 10.1016/0304-4157(92)90040-h] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- T Zeuthen
- Department of General Physiology and Biophysics, The Panum Institute, Copenhagen, Denmark
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Lyall V, Corcia A, Croxton TL, Chao AC, Armstrong WM. A possible relationship between KCl symport and basolateral K+-conductance in Necturus gallbladder epithelial cells. ACTA ACUST UNITED AC 1992; 102:497-505. [PMID: 1359939 DOI: 10.1016/0300-9629(92)90201-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
1. Apical membrane potential (Va), transepithelial potential (VT), fractional apical voltage ratio (FVa = delta Va/delta VT), tissue resistance (RT), and intracellular Cl- (aiCl) and K+ (aiK) activities were measured in isolated gallbladders maintained between oxygenated bicarbonate-free physiological media (23 degrees C, pH 7.2 or 8.2) in a divided chamber. The basolateral membrane potential (Vb) was calculated from the measured values of Va and VT. 2. Cl- removal from the serosal medium (which should accelerate coupled basolateral KCl exit) significantly depolarized Vb, decreased aiCl, decreased FVa, increased RT, and attenuated the depolarization of Vb (delta Vb) induced by high K+ added to the serosal side. These changes are consistent with a decrease in the K(+)-conductance of the basolateral membrane (gbK). 3. Addition of furosemide (an inhibitor of KCl cotransport) to the serosal medium induced significant increases in Vb, FVa, and high K(+)-induced delta Vb, indicating an increase in gbK. 4. In the presence of serosal furosemide, Cl- removal from the serosal medium did not significantly alter Vb, aiCl or delta Vb from their corresponding values when serosal Cl- was present. 5. Serosal furosemide had no significant effect on aiK and aiCl measured with double-barreled ion-selective microelectrodes. 6. These results suggest the possibility of a reciprocal relationship between gbK and the rate of basolateral KCl cotransport. This may contribute to the maintenance of aiK in gallbladder epithelial cells.
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Affiliation(s)
- V Lyall
- Department of Physiology and Biophysics, Indiana University School of Medicine, Indianapolis 46223
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Altenberg GA, Stoddard JS, Reuss L. Electrophysiological effects of basolateral [Na+] in Necturus gallbladder epithelium. J Gen Physiol 1992; 99:241-62. [PMID: 1613485 PMCID: PMC2216613 DOI: 10.1085/jgp.99.2.241] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
In Necturus gallbladder epithelium, lowering serosal [Na+] ([Na+]s) reversibly hyperpolarized the basolateral cell membrane voltage (Vcs) and reduced the fractional resistance of the apical membrane (fRa). Previous results have suggested that there is no sizable basolateral Na+ conductance and that there are apical Ca(2+)-activated K+ channels. Here, we studied the mechanisms of the electrophysiological effects of lowering [Na+]s, in particular the possibility that an elevation in intracellular free [Ca2+] hyperpolarizes Vcs by increasing gK+. When [Na+]s was reduced from 100.5 to 10.5 mM (tetramethylammonium substitution), Vcs hyperpolarized from -68 +/- 2 to a peak value of -82 +/- 2 mV (P less than 0.001), and fRa decreased from 0.84 +/- 0.02 to 0.62 +/- 0.02 (P less than 0.001). Addition of 5 mM tetraethylammonium (TEA+) to the mucosal solution reduced both the hyperpolarization of Vcs and the change in fRa, whereas serosal addition of TEA+ had no effect. Ouabain (10(-4) M, serosal side) produced a small depolarization of Vcs and reduced the hyperpolarization upon lowering [Na+]s, without affecting the decrease in fRa. The effects of mucosal TEA+ and serosal ouabain were additive. Neither amiloride (10(-5) or 10(-3) M) nor tetrodotoxin (10(-6) M) had any effects on Vcs or fRa or on their responses to lowering [Na+]s, suggesting that basolateral Na+ channels do not contribute to the control membrane voltage or to the hyperpolarization upon lowering [Na+]s. The basolateral membrane depolarization upon elevating [K+]s was increased transiently during the hyperpolarization of Vcs upon lowering [Na+]s. Since cable analysis experiments show that basolateral membrane resistance increased, a decrease in basolateral Cl- conductance (gCl-) is the main cause of the increased K+ selectivity. Lowering [Na+]s increases intracellular free [Ca2+], which may be responsible for the increase in the apical membrane TEA(+)-sensitive gK+. We conclude that the decrease in fRa by lowering [Na+]s is mainly caused by an increase in intracellular free [Ca2+], which activates TEA(+)-sensitive maxi K+ channels at the apical membrane and decreases apical membrane resistance. The hyperpolarization of Vcs is due to increase in: (a) apical membrane gK+, (b) the contribution of the Na+ pump to Vcs, (c) basolateral membrane K+ selectivity (decreased gCl-), and (d) intraepithelial current flow brought about by a paracellular diffusion potential.
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Affiliation(s)
- G A Altenberg
- Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston 77550
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Cotton CU, Reuss L. Electrophysiological effects of extracellular ATP on Necturus gallbladder epithelium. J Gen Physiol 1991; 97:949-71. [PMID: 1713948 PMCID: PMC2216508 DOI: 10.1085/jgp.97.5.949] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The effects of addition of ATP to the mucosal bathing solution on transepithelial, apical, and basolateral membrane voltages and resistances in Necturus gallbladder epithelium were determined. Mucosal ATP (100 microM) caused a rapid hyperpolarization of both apical (Vmc) and basolateral (Vcs) cell membrane voltages (delta Vm = 18 +/- 1 mV), a fall in transepithelial resistance (Rt) from 142 +/- 8 to 122 +/- 7 omega.cm2, and a decrease in fractional apical membrane resistance (fRa) from 0.93 +/- 0.02 to 0.83 +/- 0.03. The rapid initial hyperpolarization of Vmc and Vcs was followed by a slower depolarization of cell membrane voltages and a lumen-negative change in transepithelial voltage (Vms). This phase also included an additional decrease in fRa. Removal of the ATP caused a further depolarization of membrane voltages followed by a hyperpolarization and then a return to control values. fRa fell to a minimum after removal of ATP and then returned to control values as the cell membrane voltages repolarized. Similar responses could be elicited by ADP but not by adenosine. The results of two-point cable experiments revealed that ATP induced an initial increase in cell membrane conductance followed by a decrease. Transient elevations of mucosal solution [K+] induced a larger depolarization of Vmc and Vcs during exposure to ATP than under control conditions. Reduction of mucosal solution [Cl-] induced a slow hyperpolarization of Vmc and Vcs before exposure to ATP and a rapid depolarization during exposure to ATP. We conclude that ATP4- is the active agent and that it causes a concentration-dependent increase in apical and basolateral membrane K+ permeability. In addition, an apical membrane electrodiffusive Cl- permeability is activated by ATP4-.
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Affiliation(s)
- C U Cotton
- Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston 77550
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Butler DG, Youson JH, Campolin E. Configuration of the medial and lateral segments of duck (Anas platyrhynchos) salt glands. J Morphol 1991; 207:201-210. [DOI: 10.1002/jmor.1052070211] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Calcium mobilization by cadmium or decreasing extracellular Na+ or pH in coronary endothelial cells. Exp Cell Res 1991; 192:22-31. [PMID: 1984413 DOI: 10.1016/0014-4827(91)90152-k] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Replacing extracellular Na+ with choline transiently increased cytoplasmic free Ca2+ ([Ca2+]i) more than 5-fold in coronary endothelial cells. Removing external Na+ stimulated 45Ca2+ efflux approximately 4-fold and influx approximately 1.7-fold. The stimulation of efflux was independent of extracellular Ca2+ and the osmotic Na+ substitute. The release of stored Ca2+, rather than Ca2+ influx via Na(+)-Ca2+ exchange, probably causes the increase in [Ca2+]i and 45Ca2+ efflux. Cadmium or decreasing external, not intracellular, pH transiently increased [Ca2+]i. Cd2+ and some other divalent metals also stimulated 45Ca2+ efflux. The potency order of the metals that stimulated efflux was Cd2+ greater than CO2+ greater than Ni2+ greater than Fe2+ greater than Mn2+. Incubating the cells with Zn2+ prior to assaying efflux in the absence of Zn2+ strongly inhibited the stimulation of 45Ca2+ efflux by Cd2+, pH 6, and the removal of external Na+ without affecting the stimulation of efflux by ATP. These findings support the hypothesis that certain trace metals or decreasing external Na+ or pH trigger the release of stored Ca2+ by stimulating a cell surface "receptor."
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Altenberg GA, Reuss L. Apical membrane Na+/H+ exchange in Necturus gallbladder epithelium. Its dependence on extracellular and intracellular pH and on external Na+ concentration. J Gen Physiol 1990; 95:369-92. [PMID: 2307961 PMCID: PMC2216320 DOI: 10.1085/jgp.95.2.369] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Intracellular microelectrode techniques and extracellular pH measurements were used to study the dependence of apical Na+/H+ exchange on mucosal and intracellular pH and on mucosal solution Na+ concentration ([Na+]o). When mucosal solution pH (pHo) was decreased in gallbladders bathed in Na(+)-containing solutions, aNai fell. The effect of pHo is consistent with titration of a single site with an apparent pK of 6.29. In Na(+)-depleted tissues, increasing [Na+]o from 0 to values ranging from 2.5 to 110 mM increased aNai; the relationship was well described by Michaelis-Menten kinetics. The apparent Km was 15 mM at pHo 7.5 and increased to 134 mM at pHo 6.5, without change in Vmax. In Na(+)-depleted gallbladders, elevating [Na+]o from 0 to 25 mM increased aNai and pHi and caused acidification of a poorly buffered mucosal solution upon stopping the superfusion; lowering pHo inhibited both apical Na+ entry and mucosal solution acidification. Both effects can be ascribed to titration of a single site; the apparent pK's were 7.2 and 7.4, respectively. Diethylpyrocarbonate (DEPC), a histidine-specific reagent, reduced mucosal acidification by 58 +/- 4 or 39 +/- 6% when exposure to the drug was at pHo 7.5 or 6.5, respectively. Amiloride (1 mM) did not protect against the DEPC inhibition, but reduced both apical Na+ entry and mucosal acidification by 63 +/- 5 and 65 +/- 9%, respectively. In the Na(+)-depleted tissues mean pHi was 6.7. Cells were alkalinized by exposure to mucosal solutions containing high concentrations of nicotine or methylamine. Estimates of apical Na+ entry at varying pHi, upon increasing [Na+]o from 0 to 25 mM, indicate that Na+/H+ exchange is active at pHi 7.4. Intracellular H+ stimulated apical Na+ entry by titration of more than one site (apparent pK 7.1, Hill coefficient 1.7). The results suggest that external Na+ and H+ interact with one site of the Na+/H+ exchanger and that cytoplasmic H+ acts on at least two sites. The external titratable group seems to be an imidazolium, which is apparently different from the amiloride-binding site. The dependence of Na+ entry on pHi supports the notion that the Na+/H+ exchanger is operational under normal transport conditions.
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Affiliation(s)
- G A Altenberg
- Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston 77550
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