title: Acidification stimulates chloride and fluid absorption across frog retinal pigment epithelium.
abstract: Radioactive tracers and a modified capacitance-probe technique were used to characterize the mechanisms that mediate Cl and fluid absorption across the bullfrog retinal pigment epithelium (RPE)-choroid. In control (HCO3/CO2) Ringer solution, 36Cl was actively absorbed (retina to choroid) at a mean rate of 0.34 mu eq.cm-2.h-1 (n = 34) and accounted for approximately 25% of the short-circuit current. Apical bumetanide (100 microM) or basal 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; 1 mM) inhibited active Cl transport by 70 and 62%, respectively. Active Cl absorption was doubled, either by removing HCO3 from the bathing media or by elevating CO2 from 5 to 13%, and the increased flux was inhibited by apical bumetanide or basal DIDS. Open-circuit measurements of fluid absorption rate (Jv) and the net fluxes of 36Cl, 22Na, and 86Rb (K substitute) indicated that CO2-induced acidification stimulated NaCl and fluid absorption across the RPE. During acidification, bumetanide produced a twofold larger inhibition of Jv compared with control. Stimulation of net Cl absorption was most likely caused by inhibition of the the basolateral membrane intracellular pH-dependent Cl-HCO3 exchanger.
authors.affiliation: School of Optometry, University of California, Berkeley 94720.
authors.forename: J L
authors.initials: JL
authors.lastname: Edelman
authors.forename: H
authors.initials: H
authors.lastname: Lin
authors.forename: S S
authors.initials: SS
authors.lastname: Miller
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000042:Absorption / Q000187:drug effects; D000143:Acids / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000818:Animals; D002034:Bumetanide / Q000494:pharmacology; D002245:Carbon Dioxide / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism*; D004553:Electric Conductivity; D007552:Isotonic Solutions / Q000494:pharmacology; D010857:Pigment Epithelium of Eye / Q000378:metabolism* / Q000502:physiology; D011892:Rana catesbeiana; D000077331:Ringer's Solution; D012964:Sodium / Q000378:metabolism
chemical_list: D000143:Acids; D002712:Chlorides; D007552:Isotonic Solutions; D002034:Bumetanide; D002245:Carbon Dioxide; D000077331:Ringer's Solution; D012964:Sodium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid