The COOH-terminal octapeptide of cholecystokinin (CCK-OP) and carbamylcholine each increased calcium outflux, cellular cyclic GMP and amylase secretion in dispersed guinea pig pancreatic acinar cells. Following addition of CCK-OP or carbamylcholine, cellular cyclic GMP increased as early as 15 s, became maximal after 1 to 2 min, and then decreased steadily during the subsequent incubation. For both CCK-OP and carbamylcholine there was close agreement between the dose-response curve for stimulation of calcium outflux and that for increase of cellular cyclic GMP. With CCK-OP an effect on both functions could be detected at 10(-10) M and maximal stimulation occurred at 3 X 10(-8) M. With carbamylcholine an effect on both functions could be detected at 10(-5) M and maximal stimulation occurred at 3 X 10(-3) M. Atropine inhibited stimulation of both cyclic GMP and calcium outflux by carbamylcholine but not by CCK-OP. Stimulation of calcium outflux or cellular cyclic GMP by CCK-OP or carbamylcholine did not require extracellular calcium since stimulation occurred in a calcium-free, ethylene glycol bis(beta, beta-aminoethyl ether) N,N'-tetraacetic acid (EGTA)-containing solution. The divalent cation ionophore A-23187 increased bidirectional fluxes of calcium, cellular cyclic GMP and secretion of amylase from dispersed pancreatic acinar cells. Like CCK-OP and carbamylcholine, the ionophore stimulated calcium outflux and cellular cyclic GMP in a calcium-free, EGTA-containing solution. These results suggest that in pancreatic acinar cells the initial step in the sequence of events mediating the action of ionophore as well as that of CCK-OP and carbamylcholine is stimulation of calcium outflux, and that this stimulation then increases cellular cyclic GMP.