Effect of A23187 on amylase release from dispersed acini prepared from guinea pig pancreas

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Abstract
In a Ca-containing medium, A23187 increased amylase from dispersed pancreatic acini, caused persistent potentiation of the stimulation of amylase release caused by secretagogues whose actions are mediated by cyclic AMP, and inhibited the stimulation of enzyme release caused by more effective secretagogues whose actions are mediated by mobilization of cellular Ca. In a Ca-free medium, the actions of A23187 on amylase release during the 1st 10 min of incubation were the same as they were in a Ca-containing medium. After 10 min of incubation, however, A23187 did not stimulate amylase release and abolished the stimulation caused by all other secretagogues tested. A23187 caused transient stimulation of the initial uptake of 45Ca by pancreatic acini, caused a persistent 30% decrease in the steady-state cellular 45Ca and increased outflux of 45Ca. The A23187-induced increase in 45Ca outflux did not depend on extracellular Ca. A23187 appears to fix the Ca-transport system in a rapidly exchanging state and by so doing stabilizes the secretory process in such a way that it is not susceptible to alteration by other secretagogues that act by altering Ca transport but can be augmented by secretagogues that act by increasing cellular cyclic AMP. In the absence of extracellular Ca, A23187 causes an initial stimulation of enzyme release; however, after 10 min of incubation, the acini are completely depleted of exchangeable cellular Ca and there is no stimulation of amylase release by the ionophore or any other secretagogue.

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