Cl- permeability of the basolateral membrane of the Rana esculenta epithelium: activation of Cl-/HCO3- exchange by alkaline intracellular pH.
We have investigated Cl- transport mechanism(s) located in the basolateral membranes of the frog skin epithelium and in particular activation of Cl-/HCO3- exchange following an alkaline load. We found that 87% of the total 36Cl uptake by the epithelial cells occurs across the basolateral membranes (JbCl-) and submitting the epithelium to an alkaline load (HCO3(-)-Ringer solution, pH 8.1) increased JbCl-. Intracellular Cl- activity (aiCl-), measured with ion-sensitive microelectrodes, increased when the Ringer solution bathing the basolateral membranes was changed from a Ringer solution equilibrated in air (pH 7.4) to one containing CO2/HCO3- (pH 7.4). pHi recovery following an alkaline load was dependent on Cl- since it did not occur in serosal Cl(-)-free media, indicating the presence of a Cl(-)-dependent regulatory mechanism. Acid loading of the epithelial cells (5% CO2, HCO3(-)-free Ringer) produced no change in JbCl- but stimulated an amiloride-sensitive 22Na uptake across the basolateral membranes of the epithelium, compatible with an activation of a Na+/H+ exchanger, previously described in this tissue. JbCl- was partially blocked by SITS (5 x 10(-4) mmol/I), niflumic acid (5 x 10(-5) mmol/I), furosemide or bumetanide. Simultaneous addition of furosemide and niflumic acid produced an inhibition of JbCl- which was not different with furosemide alone. Substitution of Na+ by choline had no effect on JbCl- and furosemide did not block the 22Na+ uptake, suggesting that JbCl- is not a Na(+)-dependent process (cotransport). We conclude that a significant Cl- permeability at the basolateral membranes of the epithelial cells is due to the presence of a Cl-/HCO3- exchanger which is essential for the recovery of pHi following an alkaline load.
Lacoste
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Département de Biologie du C.E.A., Laboratoire Jean Maetz, Villefrance-sur-Mer, France.
Harvey
B J
BJ
Ehrenfeld
J
J
D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism; D002463:Cell Membrane Permeability; D002712:Chlorides / Q000378:metabolism*; D004848:Epithelium / Q000502:physiology / Q000648:ultrastructure; D005665:Furosemide / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D009544:Niflumic Acid / Q000494:pharmacology; D011893:Rana esculenta; D012867:Skin / Q000378:metabolism* / Q000648:ultrastructure; D017923:Sodium-Hydrogen Exchangers
D001639:Bicarbonates; D002352:Carrier Proteins; D002712:Chlorides; D017923:Sodium-Hydrogen Exchangers; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D009544:Niflumic Acid; D005665:Furosemide