Cl- channel blockers inhibit acid secretion in rabbit parietal cells

Mechanisms of gastric parietal cell secretory membrane Cl- transport and the role of this Cl- transport in acid secretion were investigated by examining the effects of two Cl- channel blockers, diphenylamine-2-carboxylate (DPC) and 9-anthracene carboxylate (9-AC) on acid secretion using isolated, enriched rabbit parietal cells. Resting and stimulated acid secretion in intact cells (measured as [14C]aminopyrine accumulation) was inhibited by DPC and 9-AC, irrespective of agonist used. Apparent inhibition constants (Ki) were 2.4 x 10(-4) M for DPC and 1.2 x 10(-3) M for 9-AC for all responses. Digitonin-permeabilized parietal cells were used to bypass possible inhibitory effects of these compounds on basolateral membrane transport processes and to investigate effects only on the secretory membrane. Both blockers inhibited ATP-driven acid secretion in resting and stimulated permeable cells with apparent Ki values in the same range as measured in intact cells, suggesting that the site of action of these blockers is at the secretory membrane. H(+)-K(+)-ATPase activity in situ in permeable parietal cells, measured as 2-methyl-8-(phenylmethoxy)imidazo(1,2) pyridine-3-acetonitrile (SCH28080)-inhibitable ATP hydrolysis, was higher in stimulated compared with resting cells. Addition of 10 mM NH4Cl abolished this difference, and maximal H(+)-K(+)-ATPase activity was measured. SCH28080 and NH4Cl each abolished both resting and stimulated acid accumulation. DPC and 9-AC inhibited resting and stimulated H(+)-K(+)-ATPase activities, without exerting inhibitory effects on the enzyme itself, since the blockers had no effect on maximal NH4(+)-stimulated H(+)-K(+)-ATPase activity.(ABSTRACT TRUNCATED AT 250 WORDS)