Calcium involvement in the muscarinic response of the gastric parietal cell

The influence of extracellular Ca 2+ on the mediation of carbachol stimulation in isolated rabbit gastric parietal cells was studied. Removing Ca 2+ from extracellular medium caused a 42% decrease of the aminopyrine accumulation due to carbachol with the same EC 50 value (∼ 5 μM). A short time depletion in extracellular calcium suppressed the carbachol-dependent Ca 2+ influx without affecting Ca 2+ release from internal stores (fura-2 measurements). Similarly, the production of inositol phosphates under cholinergic stimulation was reduced by 29%. A rapid increase in Ins(1, 4, 5)P 3 was obtained 5 s after carbachol stimulation, and this increase was not changed in Ca 2+-dependent medium. In contrast, a 20 min incubation with carbachol caused a 50% reduction in both basal and carbachol-stimulated inositol phosphate accumulations. In conclusion, phospholipase C activation, intracellular Ca 2+ release and aminopyrine accumulation were sequentially observed following carbachol stimulation of the isolated gastric parietal cell and extracellular calcium contributed to sustain this acid secretory response.