Pancreatic acinar cells: acetylcholine-induced membrane depolarization, calcium efflux and amylase release.

1. The effects of acetylcholine upon the output of amylase, Ca(2+) efflux and membrane potential of pancreatic acinar cells have been measured in segments of mouse pancreas superfused in vitro.2. Amylase output was measured continuously using an on-line automated fluorimetric method; Ca(2+) efflux was monitored by measuring the release of (45)Ca(2+) from pre-labelled tissue; and intracellular recordings of acinar transmembrane potentials were obtained with glass micro-electrodes. In some experiments membrane potentials, and in others (45)Ca(2+) efflux, were measured concomitantly with amylase release.3. Acetylcholine depolarized the acinar cells, increased tissue (45)Ca(2+) efflux and raised amylase output, each with a similar dose-dependence, i.e. a maximal response at 10(-5)M, threshold =/< 10(-8)M, and ED(50) values of 0.7 x 10(-7)M, 0.5 x 10(-7)M, and 2 x 10(-7)M for depolarization, amylase release, and (45)Ca(2+) efflux, respectively.4. In response to acetylcholine both depolarization and (45)Ca(2+) efflux preceded or coincided with the increase in amylase output.5. Acetylcholine 10(-5)M and [K](0) 47 mM were without effect on (45)Ca(2+) efflux in the presence of atropine (3 x 10(-6)M) but pancreozymin (0.3 u./ml.) still elicited a marked increase in (45)Ca(2+) release.6. These results suggest that the stimulatory action of acetylcholine on the pancreatic acinar cell involves, sequentially, a specific receptor-activated increase in membrane permeability, depolarization, Ca(2+) mobilization and amylase release. These events are discussed in relation to the integrated mechanism of stimulus-secretion coupling.