RELATIONSHIP BETWEEN SHORT-CIRCUIT CURRENT AND UNIDIRECTIONAL FLUXES OF NA AND C1 ACROSS THE CILIARY EPITHELIUM OF THE TOAD - DEMONSTRATION OF ACTIVE C1 TRANSPORT

The unidirectional fluxes of Na+ and Cl- across the isolated toad ciliary epithelium were measured under short-circuit conditions. In a normal medium, the transepithelial potential difference was about 4 mV, the epithelial side being negative with respect to the stroma side. The short-circuit current (SCC) was 46 μA/cm2 and the average electrical conductance was 11 mmhos/cm2. Both the Na+ and Cl- fluxes from the stromal to epithelial side were greater than those in the opposite direction and the net Cl- flux was 4 to 5 times greater than the net Na+ flux. In the stromal tirection, both the Na+ and Cl- fluxes were linearly related to the SCC, and the sum of the partial ionic conductances of Na+ and Cl- exceeded the electrical conductance. No correlation between the SCC and the Cl- or Na+ flux was found in the opposite direction and the sum of the partial ionic conductance agreed well with the electrical conductance. In the presence of either theophylline in 10 mm or ouabain in 1 mm, the SCC was decreased by about 70% and unidirectional fluxes of either direction were increased in accordance with the increase in the electrical conductance, except for the stromal to epithelial Cl- and Na+ fluxes in the presence of theophylline and ouabain, respectively. The data indicate that electrogenic Cl- transport is the major function and the major source of the SCC in the epithelium. © 1979.