Intracellular chloride activities in rabbit gallbladder: Direct evidence for the role of the sodium-gradient in energizing “Uphill” chloride transport

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Abstract
Intracellular chloride activities, (Cl)c, in rabbit gallbladder were determined by using conventional (KCl-filled) microelectrodes and Cl-selective, liquid ionexchanger, microelectrodes. The results indicate that in the presence of a normal Ringer's solution, (Cl)c averages 35 mM; this value is 2.3 times that predicted for an equilibrium distribution across the mucosal and baso-lateral membranes. On the other hand, when the tissue is bathed by Na-free solutions, (Cl)c declines to a value that does not differ significantly from that predicted for an equilibrium distribution. These results, together with those of Frizzellet al. (J. Gen. Physiol. 65:769, 1975) provide, for the first time, compelling evidence that (i) the movement of Cl from the mucosal solution into the cell is directed against an electrochemical potential difference (23 mV); and (ii) this movement is energized by coupling to the entry of Na down a steep electrochemical potential difference. Finally, our data suggest that (i) Cl exit from the cell across the basolateral membrane may be coupled to the co-transport of a cation or the countertransport of an anion; and (ii) the mechanism responsible for active Na extrusion from the cell across the baso-lateral membrane is rheogenic (electrogenic), and is not the result of a neutral Na-K exchange.