Electrical nature of active chloride transport across short-circuited turtle bladders

Abstract

In sodium-free ambient media, the serosa of the isolated turtle bladder becomes electronegative to the mucosa by 10-70 mv; and short-circuiting is achieved by passing positive current from serosa to mucosa. When bladders were bathed on both surfaces by choline-Ringer solution (containing bicarbonate), net chloride current (ICl) estimated from isotope fluxes accounted for 50% of the short-circuiting current (Isc) of 35.6[mu]a. After replacing the mucosal fluid with a bicarbonate-free solution (choline chloride), ICl = Isc = 20 [mu]a, on the average. Thus, chloride and bicarbonate can account for all of the short-circuiting current across bladders in a sodium-free ambient system. Changing ambient fluids to sodium-rich fluids, Isc and PD reversed in orientation and increased in magnitude, whereas tissue conductance doubled. At the same time, ICl remained constant in magnitude and direction. Therefore, active transport of chloride was independent of all ambient sodium and of mucosal bicarbonate[long dash]a behavior which follows to a first approximation the principle of independence of parallel elements in simple electrical networks.