Electrogenic bicarbonate secretion in the turtle bladder: Apical membrane conductance characteristics

1991 ◽  
Vol 119 (3) ◽  
pp. 241-252 ◽  
Author(s):  
Adam Rich ◽  
Troy E. Dixon ◽  
Chris Clausen
Keyword(s):  
Apical Membrane ◽  
Membrane Conductance ◽  
Bicarbonate Secretion ◽  
Turtle Bladder

Ba2+, TEA+, and quinine effects on apical membrane K+ conductance and maxi K+ channels in gallbladder epithelium

1990 ◽  
Vol 259 (1) ◽  
pp. C56-C68 ◽  
Author(s):  
Y. Segal ◽  
L. Reuss
Keyword(s):  
Apical Membrane ◽  
Membrane Conductance ◽  
Membrane Resistance ◽  
K Channel ◽  
Dependent Manner ◽  
Gallbladder Epithelium ◽  
Concentration Dependent Manner ◽  
K Channels ◽  
Voltage Dependent ◽  
Channel Currents

The apical membrane of Necturus gallbladder epithelium contains a voltage-activated K+ conductance [Ga(V)]. Large-conductance (maxi) K+ channels underlie Ga(V) and account for 17% of the membrane conductance (Ga) under control conditions. We examined the Ba2+, tetraethylammonium (TEA+), and quinine sensitivities of Ga and single maxi K+ channels. Mucosal Ba2+ addition decreased resting Ga in a concentration-dependent manner (65% block at 5 mM) and decreased Ga(V) in a concentration- and voltage-dependent manner. Mucosal TEA+ addition also decreased control Ga (60% reduction at 5 mM). TEA+ block of Ga(V) was more potent and less voltage dependent that Ba2+ block. Maxi K+ channels were blocked by external Ba2+ at millimolar levels and by external TEA+ at submillimolar levels. At 0.3 mM, quinine (mucosal addition) hyperpolarized the cell membranes by 6 mV and reduced the fractional apical membrane resistance by 50%, suggesting activation of an apical membrane K+ conductance. At 1 mM, quinine both activated and blocked K(+)-conductive pathways. Quinine blocked maxi K+ channel currents at submillimolar concentrations. We conclude that 1) Ba2+ and TEA+ block maxi K+ channels and other K+ channels underlying resting Ga; 2) parallels between the Ba2+ and TEA+ sensitivities of Ga(V) and maxi K+ channels support a role for these channels in Ga(V); and 3) quinine has multiple effects on K(+)-conductive pathways in gallbladder epithelium, which are only partially explained by block of apical membrane maxi K+ channels.

Ion transport in goby intestine: cellular mechanism of urotensin II stimulation

1985 ◽  
Vol 249 (2) ◽  
pp. G284-G293
Author(s):  
C. A. Loretz ◽  
M. E. Howard ◽  
A. J. Siegel
Keyword(s):  
Apical Membrane ◽  
Apical Cell ◽  
Phosphodiesterase Inhibitor ◽  
Membrane Conductance ◽  
Urotensin Ii ◽  
Apical Cell Membrane ◽  
Absorptive Cells ◽  
Ion Substitution ◽  
Columnar Cells ◽  
Leaky Epithelium

The Na- and Cl-absorbing goby posterior intestinal epithelium is composed predominantly of mitochondria-rich, tall columnar cells. Glass intracellular microelectrode recording technique was applied to absorptive cells of this relatively leaky epithelium to measure apical cell membrane potential difference (psi mc) and apical membrane fractional resistance. As determined by ion-substitution studies, absorptive cells are characterized by a large, Ba2+-inhibitable apical K conductance, which is a major factor determining psi mc and smaller Cl and Na conductances. Inhibition of the apical Na-Cl-coupled influx directly by furosemide or indirectly by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine produced hyperpolarization of psi mc, consistent with the greater apical membrane conductance to Cl than Na. The urophysial neurosecretory peptide urotensin II, which stimulates Na-Cl-coupled absorption, markedly depolarized psi mc in posterior intestinal tissues from 5% seawater-adapted gobies. This response is consistent with a stimulatory effect of urotensin II at the apical membrane carrier rather than at the basolateral Na-K-ATPase. Urotensin II is without effect on psi mc in tissues from seawater-adapted fish and somatostatin, a natural analogue of urotensin II, is without effect on tissues from fish adapted to either salinity. This specificity parallels that determined using radiotracer fluxes.

EGF and PGE2 inhibit rabbit CCD Na+ transport by different mechanisms: PGE2 inhibits Na(+)-K+ pump

1993 ◽  
Vol 264 (4) ◽  
pp. F670-F677 ◽  
Author(s):  
D. H. Warden ◽  
J. B. Stokes
Keyword(s):  
Apical Membrane ◽  
Collecting Duct ◽  
Basolateral Membrane ◽  
Membrane Conductance ◽  
Membrane Voltage ◽  
Na Channel ◽  
Cortical Collecting Duct ◽  
Na Transport ◽  
Flux Measurements ◽  
Epidermal Growth

The rabbit cortical collecting duct absorbs Na+ by a transport system comprised of an apical membrane Na+ channel and a basolateral membrane Na(+)-K(+)-adenosinetriphosphatase. The rate of Na+ absorption across this epithelium is acutely inhibited by several hormones and autacoids including epidermal growth factor (EGF) and prostaglandin E2 (PGE2). We used electrophysiological analysis to determine which Na+ transport mechanism is primarily regulated in response to EGF and PGE2. We used concentrations of EGF and PGE2 that inhibited Na+ absorption to a comparable degree. We assessed the effects of these agents on Na+ transport primarily by the calculated equivalent current; the validity of this indicator was verified using simultaneous tracer flux measurements. EGF and PGE2 had different effects on the intracellular electrophysiological parameters. EGF (in the presence of a cyclooxygenase inhibitor) hyperpolarized the apical membrane voltage in a manner analogous to the Na(+)-channel blocker amiloride, reduced the transepithelial conductance, and increased the fractional resistance of the apical membrane. In comparison, PGE2 depolarized the apical membrane voltage in a manner analogous to the Na(+)-K+ pump inhibitor ouabain, and caused no significant changes in transepithelial conductance or apical membrane conductance. The finding that EGF hyperpolarized the apical membrane indicates that this agent attenuates Na+ absorption by reducing apical Na+ entry due to a decrease in the magnitude of the apical membrane Na+ conductance. In contrast, the electrophysiological changes produced by PGE2 indicate primary inhibition of the basolateral Na(+)-K+ pump following PGE2 treatment.

Effect of Slc26a6 deletion on apical Cl−/HCO3− exchanger activity and cAMP-stimulated bicarbonate secretion in pancreatic duct

2007 ◽  
Vol 292 (1) ◽  
pp. G447-G455 ◽  
Author(s):  
Hiroshi Ishiguro ◽  
Wan Namkung ◽  
Akiko Yamamoto ◽  
Zhaohui Wang ◽  
Roger T. Worrell ◽  
...  
Keyword(s):  
Pancreatic Duct ◽  
Apical Membrane ◽  
Pancreatic Ducts ◽  
Bicarbonate Secretion ◽  
Wild Type ◽  
Rt Pcr ◽  
Secretory Rate ◽  
Transport Fluid ◽  
Exchange Activity

The role of Slc26a6 (PAT1) on apical Cl−/HCO3− exchange and bicarbonate secretion in pancreatic duct cells was investigated using Slc26a6 null and wild-type (WT) mice. Apical Cl−/HCO3− exchange activity was measured with the pH-sensitive dye BCECF in microperfused interlobular ducts. The HCO3−-influx mode of apical [Cl−]i/[HCO3−]o exchange (where brackets denote concentration and subscripts i and o denote intra- and extracellular, respectively) was dramatically upregulated in Slc26a6 null mice ( P < 0.01 vs. WT), whereas the HCO3−-efflux mode of apical [Cl−]o/[HCO3−]i exchange was decreased in Slc26a6 null mice ( P < 0.05 vs. WT), suggesting the unidirectionality of the Slc26a6-mediated HCO3− transport. Fluid secretory rate in interlobular ducts were comparable in WT and Slc26a6 null mice ( P > 0.05). In addition, when pancreatic juice was collected from whole animal in basal and secretin-stimulated conditions, neither juice volume nor its pH showed differences between WT and Slc26a6 null mice. Semiquantitative RT-PCR demonstrated more than fivefold upregulation in Slc26a3 (DRA) expression in Slc26a6 knockout pancreas. In conclusion, these results point to the role of Slc26a6 in HCO3− efflux at the apical membrane and also suggest the presence of a robust Slc26a3 compensatory upregulation, which can replace the function of Slc26a6 in pancreatic ducts.

scholarly journals Maxi K+ channels and their relationship to the apical membrane conductance in Necturus gallbladder epithelium.

1990 ◽  
Vol 95 (5) ◽  
pp. 791-818 ◽  
Author(s):  
Y Segal ◽  
L Reuss
Keyword(s):  
Patch Clamp ◽  
Apical Membrane ◽  
Membrane Conductance ◽  
Membrane Depolarization ◽  
Membrane Voltage ◽  
K Channel ◽  
Gallbladder Epithelium ◽  
Patch Clamp Technique ◽  
K Channels ◽  
Necturus Gallbladder

Using the patch-clamp technique, we have identified large-conductance (maxi) K+ channels in the apical membrane of Necturus gallbladder epithelium, and in dissociated gallbladder epithelial cells. These channels are more than tenfold selective for K+ over Na+, and exhibit unitary conductance of approximately 200 pS in symmetric 100 mM KCl. They are activated by elevation of internal Ca2+ levels and membrane depolarization. The properties of these channels could account for the previously observed voltage and Ca2+ sensitivities of the macroscopic apical membrane conductance (Ga). Ga was determined as a function of apical membrane voltage, using intracellular microelectrode techniques. Its value was 180 microS/cm2 at the control membrane voltage of -68 mV, and increased steeply with membrane depolarization, reaching 650 microS/cm2 at -25 mV. We have related maxi K+ channel properties and Ga quantitatively, relying on the premise that at any apical membrane voltage Ga comprises a leakage conductance and a conductance due to maxi K+ channels. Comparison between Ga and maxi K+ channels reveals that the latter are present at a surface density of 0.09/microns 2, are open approximately 15% of the time under control conditions, and account for 17% of control Ga. Depolarizing the apical membrane voltage leads to a steep increase in channel steady-state open probability. When correlated with patch-clamp studies examining the Ca2+ and voltage dependencies of single maxi K+ channels, results from intracellular microelectrode experiments indicate that maxi K+ channel activity in situ is higher than predicted from the measured apical membrane voltage and estimated bulk cytosolic Ca2+ activity. Mechanisms that could account for this finding are proposed.

scholarly journals Nystatin as a probe for investigating the electrical properties of a tight epithelium.

1977 ◽  
Vol 70 (4) ◽  
pp. 427-440 ◽  
Author(s):  
S A Lewis ◽  
D C Eaton ◽  
C Clausen ◽  
J M Diamond
Keyword(s):  
Apical Membrane ◽  
Basolateral Membrane ◽  
Membrane Conductance ◽  
Voltage Divider ◽  
Junctional Conductance ◽  
Transepithelial Voltage ◽  
Almost All ◽  
Voltage Divider Ratio ◽  
Rabbit Urinary Bladder ◽  
Tight Epithelium

We show how the antibiotic nystatin may be used in conjunction with microelectrodes to resolve transepithelial conductance Gt into its components: Ga, apical membrane conductance; Gbl, basolateral membrane conductance; and Gj, junctional conductance. Mucosal addition of nystatin to rabbit urinary bladder in Na+-containing solutions caused Gt to increase severalfold to ca. 460 micrometerho/muF, and caused the transepithelial voltage Vt to approach +50 mV regardless of its initial value. From measurements of Gt and the voltage-divider ratio as a function of time after addition or removal of nystatin, values for Ga, Gbl, and Gj of untreated bladder could be obtained. Nystatin proved to have no direct effect on Gbl or Gj but to increase Ga by about two orders of magnitude, so that the basolateral membrane then provided almost all of the electrical resistance in the transcellular pathway. The nystatin channel in the apical membrane was more permeable to cations than to anions. The dose-response curve for nystatin had a slope of 4.6. Use of nystatin permitted assessment of whether microelectrode impalement introduced a significant shunt conductance into the untreated apical membrane, with the conclusion that such a shunt was negligible in the present experiments. Nystatin caused a hyperpolarization of the basolateral membrane potential in Na+-containing solutions. This may indicate that the Na+ pump in this membrane is electrogenic.

Apical and basolateral membrane conductances in the TBM cell line

1991 ◽  
Vol 260 (6) ◽  
pp. C1172-C1181 ◽  
Author(s):  
J. D. Horisberger
Keyword(s):  
Cell Line ◽  
Epithelial Transport ◽  
Apical Membrane ◽  
Ex Vivo ◽  
Biochemical Study ◽  
Basolateral Membrane ◽  
Membrane Conductance ◽  
Cultured Cell ◽  
Membrane Conductances ◽  
Collagen Membranes

Cultured cell lines present several advantages over whole organ or ex vivo isolated epithelium for the physiological and biochemical study of epithelial transport. We have developed a new technique allowing for simultaneous intracellular and transepithelial electrophysiological measurements in the epithelium formed by a cultured cell line grown on thin collagen membranes. This technique was applied to the TBM 18/23 (toad bladder origin) cell line. The transepithelial and basolateral membrane potentials were -30 +/- 11 and -72 +/- 8 (SD) mV (n = 36), respectively. With the use of the effect of amiloride, which partially blocked the apical membrane conductance, and circuit analysis, the apical and basolateral membrane conductances were estimated to 0.7 +/- 0.1 and 2.8 +/- 0.4 mS/cm2, respectively. A sodium-selective conductive pathway was demonstrated in the apical membrane, and a barium-sensitive K(+)-selective conductance was shown to be present in the basolateral membrane. The basolateral membrane conductance was not modified by sudden inhibition of sodium transport by amiloride, but it was significantly reduced after a long-term decrease of Na+ transport. The cultured TBM cell line appears to be a convenient model to investigate the regulation of membrane ionic conductances in tight epithelia.

Sign in / Sign up

Export Citation Format

Share Document