Analysis of presteady-state Na+ fluxes across the rabbit corneal endothelium

Instead of the conventional steady-state fluxes, the presteady-state fluxes of 22Na across the rabbit corneal endothelium were measured. In contrast to reports that there is no net Na+ movement across the corneal endothelium, we find a net transport of Na+ across this tissue. The direction of net Na+ flux is from the stromal to the aqueous side and the magnitude is 2.3 +/- 0.4 mueq/cm2 X hr (n = 11, SEM). Net Na+ transport is inhibited in the presence of ouabain (10(-4) M). Acetazolamide (10(-4) M) has only a slight inhibitory effect on the rate of Na+ transport but decreases the transendothelial potential difference by about 30%. The passive component of the Na+ transport has been estimated by analyzing the presteady-state influx and efflux curves and found to occur 10% via cellular and 90% via paracellular routes. The analysis for the separation of the pathways has been based on a recently proposed theory which holds that the flux ratio, regardless of its driving forces, is independent of time.