HCO3- transport in the toad lens epithelium is mediated by an electronegative Na(+)-dependent symport.
The pH-sensitive cell-entrapable dye 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF) was used to continuously monitor epithelial intracellular pH (pHi) of intact toad lenses, enabling a description of a HCO3- transport mechanism that contributes to pHi homeostasis of this organ. In physiological medium, pH 7.40, the steady-state pHi was 7.48 +/- 0.03 (SE; n = 93). Induction of cell depolarization by either elevation of [K+] to 50 mM, addition of 0.2 mM quinidine, a K(+)-channel blocker, or addition of 0.1 mM Li+ ionophore that equalizes Na+ and K+ permeabilities elicited pHi increases (delta pHi = 0.18 +/- 0.02; P less than 0.0005; n = 13, for K+). These increases could be blocked or reverted by DIDS and were not affected by amiloride. Removal of Na+ induced an amiloride-insensitive acidification. pHi recovery seen upon Na+ reintroduction in the presence of amiloride was inhibited by DIDS. Despite the effects of DIDS on induced pHi changes, the agent did not affect control pHi. Elevation of medium HCO3- (pH to 7.7) produced a pHi increase followed by a spontaneous reversal. This increase was both DIDS and Na+ sensitive. pHi was not affected in any condition by removal (or addition) of Cl-, unless the lens was pretreated with the artificial Cl(-)-HCO3- exchanger tributyltin. Collectively, these results suggest that the primary mechanism for HCO3- movement across the lens epithelial membrane is an electronegative Na+ cotransporter and that this system is near equilibrium under normal physiological conditions.
Wolosin
J M
JM
Department of Ophthalmology, Mount Sinai School of Medicine, New York, New York 10029.
Alvarez
L J
LJ
Candia
O A
OA
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002024:Bufo marinus; D002712:Chlorides / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007476:Ionophores / Q000494:pharmacology; D007700:Kinetics; D007908:Lens, Crystalline / Q000187:drug effects / Q000378:metabolism*; D011802:Quinidine / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism*
D001639:Bicarbonates; D002712:Chlorides; D007476:Ionophores; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D000584:Amiloride; D012964:Sodium; D011802:Quinidine; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid