Role of calcium in antral gastrin release

The role of calcium in gastrin release was investigated using rat antral organ culture. During the initial 4-h culture interval, in the absence of calcium in the culture medium, gastrin release was not different from that observed with 0.5, 1, and 2 mM calcium. However, after 6 h of culture, gastrin release with 0.5, 1, and 2 mM calcium was significantly greater than that with antral explants cultured in calcium-free media. In the presence of 1 mM calcium in the culture medium gastrin release was stimulated by dibutyryl cyclic AMP, whereas with calcium-free culture medium dibutyryl cyclic AMP was ineffective in stimulating gastrin release. Effects of ionophore A23187 on gastrin release were examined in experiments with culture medium containing no added calcium and with 2 mM calcium. The dose-response to ionophore A23187 (1.2--10 microgram/ml) with 2 mM calcium demonstrated progressive increases in culture media gastrin at 30, 60, and 120 min of culture. Maximal gastrin release occurred with 10 microgram/ml ionophore at each culture interval. Gastrin releases was not stimulated by increasing doses of ionophore when added to calcium-free organ culture media. Results of these experiments suggest that calcium is important in regulation of antral gastrin release and that dibutyryl cyclic AMP-stimulated release of antral gastrin is, at least in part, calcium-dependent. Stimulation of gastrin secretion by ionophore A23187 (in the presence of calcium) further supports the role of calcium in antral gastrin release and suggests that transport of calcium across cellular membranes is important in the coupling of secretory events in the gastrin cell.