Evidence for a chloride conductance in secretory membrane of parietal cells.

A fluorescence-quench method using acridine orange as the probe was employed to monitor acid formation in situ by detergent-permeabilized gastric glands. In KCl medium, the addition of ATP to the permeabilized glands resulted in a rapid decrease in fluorescence and addition of valinomycin resulted in a second phase of fluorescence quench. The fluorescence was restored by addition of the H+-K+-ATPase inhibitor, Sch 28080. An ATP-dependent fluorescence quench was observed also in K2SO4 or K+-isethionate medium; however, valinomycin was ineffective in the Cl-free media. The ATP-dependent quench could be reversed or prevented by the electrogenic protonophore, tetrachlorosalicylanilide (TCS), in KCl medium but not in Cl-free media. The results with TCS are interpreted as demonstrating a large Cl- conductance in the secretory membrane, whereas the results with valinomycin indicate that resting membranes lack a K+ conductance. The data suggest that a complex KCl pathway that may demonstrate a Cl- conductance is used to activate acid secretion.