Extracellular Calcium and Cholinergic Stimulation of

gic stimulation of the function of parietal cells was studied using cells isolated from canine fundic mucosa by treatment with collagenase and EDTA and en-riched by velocity separation in an elutriator rotor. Monitoring the accumulation of [14C]aminopyrine as an index of parietal cell response, stimulation by carbachol, but not by histamine, was highly dependent upon the concentration of extracellular calcium. Incu-bation of parietal cells in 0.1 mM calcium, rather than the usual 1.8-mM concentration, reduced the response to 100,uM carbachol by 92+±2%, whereas histamine stimulation was impaired by 28±5%. A similar reduction in extracellular calcium suppressed the response to gastrin (100 nM) by 67±7%. The im-pairment of cholinergic stimulation found at low extra-cellular calcium concentrations was rapidly reversed with the readdition of calcium. Lanthanum, which blocks calcium movement across membranes, caused a similar pattern of effects on secretagogue stim-ulation of aminopyrine accumulation, with 100,&M lanthanum suppressing carbachol stimulation by 83±2%. This concentration of lanthanum suppressed gastrin stimulation by 40±+7 % and histamine stimulation by only 12±9%. Carbachol, but not histamine nor gastrin, stim-ulated 45Ca++ uptake. The magnitude of carbachol-stimulated calcium uptake correlated with the parietal cell content of the fractions examined (r = 0.88), and was dose responsive over carbachol concentrations from 1,uM to 1 mM. Atropine (100 nM) caused surmountable inhibition, and these effects ofcarbachol and atropine on calcium uptake correlated with thei