The relationship between extracellular K+ and Ca2+ on aminopyrine accumulation in rat parietal cells

The effects of extracellular K+ in relation to extracellular Ca2+ on acid production were studied. Studies were performed in vitro using isolated cells from rat stomachs, and acid production was indirectly determined by 14C-aminopyrine (AP) accumulation. In the absence of K+ in the incubation medium histamine-stimulated AP accumulation ratios were significantly decreased independently in the presence or absence of extracellular Ca2+. Under basal conditions, in the absence of extracellular Ca2+, increasing concentrations of extracellular K+ enhanced AP accumulation ratios to significantly higher than those found in the presence of Ca2+. In histamine-, cAMP-, and carbachol-stimulated parietal cells, high K+ concentrations increased AP accumulation significantly less in Ca(2+)-free than in Ca(2+)-containing media. High K+ also induced significantly both an increase in cytosolic free Ca2+ concentration and 45Ca2+ uptake. The present results confirmed the importance of K+ in gastric acid production and suggested a role for Ca2+ as a modulator of mechanisms of parietal cell stimulation.