Endothelial bicarbonate, sodium and chloride transport: characteristics and relations to corneal deturgescence

Abstract

Unidirectional and net bicarbonate, sodium, and chlorid.e fluxes were i~otopically meas~red and characterized in the isolated rabbit corneal endothelium. Bicarbonate·and sodium fluxes were temperature dependent · o ·o · -6 over 13 -37 C, as is endothelial fluid e~trusion. Ouabain (10 M), which inhibits. the endothelial Na-K ATPase and transendothelial fluid extrusion, increased the bicarbonate permeability, ·but left net bicarbonate and sodium transport unaffec·ted. The sodium uptake inhibitor, amiloride (10-4 M) ·did not alter the net sodium or bicarbonate flux. Like endothelial fluid transport; the net sodium flux was chloride independent. Unlike fluid translocation, howev~r, the sodium transport system was .. potassium independent. Carbonic anhydrase ( 1 mg/ml), which stimulat.es endo·thelial bicarbonate transport, and acetazolamide (10..:.3 M). or 5 mM bicarbonate Ringer solt1tion, which inhibit qicarbonate transport, had no effect on the ne·t sodium flux. The net transport of chloride was unaffecte.d by sodium-.fre.e Ringer. Like bicarbonate and sodium transport, chloride transport occurs against its electrochemical gradient. The findings strongly suggest 1) that although both bicarbonate and sodium transport are sodium and bicarbonate dependent, none of the transport systems are stoichiometrica1ly coupled; and 2) tha~ the three ion: transport systems (sodium, bicarbonate and chloride) may each contribute to corne~l ~luid transport.