Characteristics of bicarbonate, sodium, and chloride fluxes in the rabbit corneal endothelium.

Unidirectional fluxes of bicarbonate, sodium and chloride were measured across the isolated rabbit corneal endothelium. Bicarbonate and sodium fluxes were measured between 13 and 37 degrees C and were found to be temperature-sensitive. Ouabain (10(-6)M), which inhibits endothelial fluid transport, reduced the net bicarbonate flux by 32% but had no significant effect on sodium fluxes. Amiloride (10(-4)M) did not alter sodium transport, but slightly increased the unidirectional bicarbonate fluxes. Sodium fluxes were unchanged in chloride-free and potassium-free Ringer solutions, and net sodium transport was unaffected in the presence of carbonic anhydrase, acetazolamide, or low (5 mM) bicarbonate Ringer, but was reduced by 45% in bicarbonate-free Ringer. A net chloride flux was found in the same direction (stroma to aqueous) as bicarbonate and sodium. This chloride flux (2.18 muEq/cm2/hr) was of the same magnitude as bicarbonate but was sodium-independent. These findings suggest that: (1) like bicarbonate and fluid transport, sodium transport is bicarbonate-dependent, temperature-sensitive, and chloride-independent; (2) sodium transport is not stoichiometrically coupled to bicarbonate; and (3) neither sodium nor bicarbonate transport are coupled to that of chloride.