Rheogenic sodium-bicarbonate co-transport across the retinal membrane of the frog retinal pigment epithelium.
1. Na+ and HCO3- transport across the retinal membrane of the frog retinal pigment epithelium was studied by means of double-barrelled Na(+)- and pH-selective microelectrodes. Transient changes in the intracellular pH and in the intracellular Na+ activity were monitored in response to abrupt changes in the Na+ concentration and in the HCO3- concentration on the retinal side of the epithelium, and in response to transepithelial currents. 2. Removal of Na+ from the retinal side of the epithelium caused a depolarization of the membrane potential across the retinal membrane, a decrease in the intracellular Na+ activity and a decrease in the intracellular pH. 3. An increase in the HCO3- concentration on the retinal side of the epithelium from 27.5 to 50 mM caused a hyperpolarization of the membrane potential across the retinal membrane, an increase in the intracellular Na+ activity and an increase in the intracellular pH. 4. Passage of a transepithelial current of 30 microA in the choroid-to-retina direction caused an increase in the intracellular Na+ activity and an increase in the intracellular pH. 5. The data are interpreted as evidence for rheogenic co-transport of Na+, HCO3- across the retinal membrane of the frog retinal pigment epithelium. 6. The transient changes described under 2, 3 and 4 above were blocked by 0.5 mM-4-acetamido-4'-isothiocyanostilbene-2.2'-disulphonic acid (SITS). The Na(+)- HCO3- co-transport was not inhibited by 1 mM-amiloride.
La Cour
M
M
Department of General Physiology and Biophysics, University of Copenhagen, Panum Institute, Denmark.
D000818:Animals; D001639:Bicarbonates / Q000493:pharmacokinetics*; D004594:Electrophysiology; D066298:In Vitro Techniques; D010857:Pigment Epithelium of Eye / Q000378:metabolism* / Q000502:physiology; D011892:Rana catesbeiana; D012964:Sodium / Q000493:pharmacokinetics*
D001639:Bicarbonates; D012964:Sodium