Gastrin and the neuropeptide PACAP evoke secretion from rat stomach histamine-containing (ECL) cells by stimulating influx of Ca2+ through different Ca2+ channels

1. Gastrin and PACAP stimulate secretion of histamine and pancreastatin fro m isolated rat stomach ECL cells. We have examined whether or not secretion depends on the free cytosolic Ca2+ concentration ([Ca2+](i)) and the pathw ays by which gastrin and PACAP elevate [Ca2+](i). Secretion was monitored b y radioimmunoassay of pancreastatin and changes in [Ca2+](i) by video imagi ng, The patch clamp technique was used to record whole-cell currents and me mbrane capacitance (reflecting exocytosis). 2 In the presence of 2 mM extracellular Ca2+; gastrin and PACAP induced sec retion and raised [Ca2+](i). Without extracellular Ca2+ (or in the presence of La3+) no secretion occurred. The extracellular Ca2+ concentration requi red to stimulate secretion was 10 times higher for gastrin than for PACAP. Depletion of intracellular Ca2+ pools by thapsigargin had no effect on the capacity of gastrin and PACAP to stimulate secretion. 3. Gastrin-evoked secretion was inhibited 60-80 % by L-type channel blocker s and 40 % by the N-type channel blocker omega -conotoxin GVIA. Combining L -type and N-type channel blockers did not result in greater inhibition than L-type channel blockers alone. Whole-cell patch clamp measurements confirm ed that the ECL cells are equipped with voltage-dependent inward Ca2+ curre nts. A 500 ms depolarising pulse from -60 mV to +10 mV which maximally open ed these channels resulted in an increase in membrane capacitance of 100 fF reflecting exocytosis of secretory vesicles. 4. PACAP-evoked secretion was reduced 40 % by L-type channel blockers but w as not influenced by inhibition of N-type channels. SXF 96365, a blocker of both L-type and receptor-operated Ca2+ channels, inhibited PACAP-evoked se cretion by 85 %. Combining L-type channel blockade with SKIP 96365 abolishe d PACAP-evoked secretion. 5. The results indicate that gastrin- and PACAP-evoked secretion depends on Ca2+ entry and not on mobilisation of intracellular Ca2+. While gastrin st imulates secretion via voltage-dependent L-type and N-type Ca2+ channels, P ACAP acts via L-type and receptor-operated Ca2+ channels.