Activation of G_q protein-coupled receptors usually causes a biphasic increase in intracellular calcium concentration ([Ca²⁺]_i) that is crucial for secretion in nonexcitable cells. In gastric enterochromaffin-like (ECL) cells, stimulation with gastrin leads to a prompt biphasic calcium response followed by histamine secretion. This study investigates the underlying signaling events in this neuroendocrine cell type. In ECL cells, RT-PCR suggested the presence of inositol 1,4,5-trisphosphate receptor (IP₃R) subtypes 1-3. The IP₃R antagonist 2-aminoethoxydiphenyl borate abolished both gastrin-induced elevation of [Ca²⁺]_i and histamine release. Thapsigargin increased [Ca²⁺]_i, however, without inducing histamine secretion. In thapsigargin-pretreated cells, gastrin increased [Ca²⁺]_i through calcium influx across the plasma membrane. Both nimodipine and SKF-96365 inhibited gastrin-induced histamine release. The protein kinase C (PKC) activator phorbol 12-myristate 13-acetate induced histamine secretion, an effect that was prevented by nimodipine. In summary, gastrin-stimulated histamine release depends on IP₃R activation and plasmalemmal calcium entry. Gastrin-induced calcium influx was mediated by dihydropyridine-sensitive calcium channels that appear to be L-type channels activated through a pathway involving activation of PKC.