title: Direct evidence for a basolateral membrane Cl- conductance in toad retinal pigment epithelium.
abstract: There is now evidence that a Cl- conductance on the basal membrane of the retinal pigment epithelium (RPE) is involved in the generation of both the fast oscillation and the light peak of the direct-current electroretinogram as well as being critical for transepithelial fluid and salt movement. In the present study, we characterized the basolateral membrane Cl- conductance of an in vitro preparation of toad RPE-choroid using conventional and Cl(-)-selective microelectrodes. Under control conditions, the potential across the apical (Vap) and basal (Vba) membranes averaged -60 +/- 2 and -45 +/- 2 mV, respectively (n = 40). Intracellular Cl- activity (aiCl = 20 +/- 1 mM) was distributed above equilibrium across both membranes, consistent with active accumulation of Cl-. A sixfold decrease in Cl- in the basal bath depolarized Vba by 12 +/- 1 mV (n = 17) and increased the apparent basal membrane resistance. By sequential measurement of aiCl and subepithelial Cl- activity during a step decrease in basal Cl-, we constructed the change in Cl- equilibrium potential (ECl) across the basal membrane. Estimation of the change in basal membrane electromotive force during the change in ECl gave an average value for the Cl- transference number (TCl) of 0.45. Further evidence for a Cl- conductance was obtained by measuring changes in aiCl induced by transepithelial current. Depolarizing Vba elevated aiCl, whereas hyperpolarizing Vba had the opposite effect, consistent with conductive Cl- movement across the basal membrane. Both the amplitude of the Cl- diffusion potential and the current-induced changes in aiCl were reduced by basal perfusion with 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (250-500 microM), a blocker of Cl- channels in some epithelia.
authors.affiliation: Department of Physiology, University of California, San Francisco 94143.
authors.forename: S
authors.initials: S
authors.lastname: Fujii
authors.forename: R P
authors.initials: RP
authors.lastname: Gallemore
authors.forename: B A
authors.initials: BA
authors.lastname: Hughes
authors.forename: R H
authors.initials: RH
authors.lastname: Steinberg
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000465:Algorithms; D000818:Animals; D002024:Bufo marinus; D018118:Chloride Channels; D002712:Chlorides / Q000502:physiology*; D004553:Electric Conductivity; D004594:Electrophysiology; D005260:Female; D007425:Intracellular Membranes / Q000502:physiology; D008297:Male; D008565:Membrane Proteins / Q000037:antagonists & inhibitors; D008839:Microelectrodes; D010857:Pigment Epithelium of Eye / Q000502:physiology*; D012016:Reference Values
chemical_list: D018118:Chloride Channels; D002712:Chlorides; D008565:Membrane Proteins; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid