SIGNAL-TRANSDUCTION EVENTS INVOLVED IN BOMBESIN-STIMULATED GASTRIN-RELEASE FROM HUMAN G-CELLS IN CULTURE

The mechanism of action of bombesin on human antral gastrin cells in c ulture was evaluated by modulating internal and external calcium level s and intracellular enzyme activities. Increasing extracellular calciu m increased basal gastrin release and had an additive effect on bombes in-stimulated gastrin release. Removing extracellular calcium had no e ffect on bombesin-stimulated gastrin release. Inhibiting the activitie s of phospholipase C by neomycin and protein kinase C by staurosporine had no effect on basal release but decreased bombesin-stimulated gast rin release by up to 50%. Chelating intracellular calcium with BAPTA-A M also decreased bombesin-stimulated release by up to 50%. Increasing intracellular calcium levels with thapsigargin did not alter basal gas trin release and had no effect on bombesin-stimulated release. The pre paration utilized was a mixed, primary cell culture. To demonstrate di rect activation of gastrin cells, alterations in internal calcium leve ls were monitored by dual-excitation microfluorometry of fura 2-AM loa ded cells. The individual cells were subsequently identified by immuno cytochemistry, confirming that bombesin directly increases calcium lev els in the G cells. The data indicated that bombesin acting directly o n the G cells activated both arms of the phosphoinositol signalling pa thway and that both activities were required for optimal gastrin relea se.