The effects of Ca'++ on release of amylase by mouse pancreas in vitri was studied. The cholinergic agonist bethanechol was depressed about 50% in O Ca'++ medium. When pancreatic fragments were superfused with O Ca'++ medium, bethanechol still produced a normal stimulation of amylase release after half of the total tissue Ca'++ was washed out. This Ca'++ loss included both extracellular and some intracellularCa'++. Uptake and equilibration of '45Ca'++ into pancreatic fragments was multiphasic, with total equilibration with stable Ca'++ still not reached after 3 h. Addition of bethanechol had no effect on the rate of '45Ca uptake and equilibration. '45Ca'++ efflux was not influenced by superfision in O Ca'++ medium, while thestimulation of '45Ca'++ efflux by bethanechol was enhanced. It is concluded that extracellular Ca'++ and/or Ca'++ influx is not of major importance in triggering pancreatic enzyme release, but that extracellular Ca'++ may regulate the release process thus accounting for the parallel changes in unstimulated and stimulated amylase release.
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Williams et al. (1975) studied this question.