INTERACTIONS OF INTRACELLULAR MEDIATORS OF AMYLASE SECRETION IN PERMEABILIZED PANCREATIC ACINI

Mouse pancreatic acini were permeabilized with streptolysin O to investigate amylase secretion stimulated by various intracellular mediators and the kinetics of secretion as a function of temperature. Amylase secretion was temperature dependent in that the initial rate of Ca2+-stimulated secretion increased with increasing temperature. In addition, there was no enhancement of Ca2+-stimulated secretion by GTP[gamma-S] at 14-degrees-C, while enhancement was maximal at 30-degrees-C. GTP[gamma-S]-mediated enhancement of secretion at a given temperature was mostly due to sustained secretion with a small increase in secretory rate. At 30-degrees-C Ca2+-stimulated secretion was also enhanced by cAMP and phorbol ester (TPA) to similar extents as by GTP[gamma-S]. The maximally effective concentration of cAMP was 1-10-mu-M in the presence of 0.1 mM isobutylmethylxanthine. The enhancements of Ca2+-stimulated amylase secretion by all combinations of cAMB (100-mu-M plus 0.1 mM isobutylmethylxanthine), TPA (1-mu-M), and GTP[gamma-S] (30-mu-M) were fully additive. In Ca2+-free buffer, cAMP, TPA or GTP[gamma-S] individually had no effect on amylase secretion. Together, TPA and GTP[gamma-S] stimulated Ca2+-independent secretion, which was 187 +/- 38% of basal. Cyclic AMP together with TPA and GTP[gamma-S] in the absence of Ca2+ stimulated 329 +/- 30% of basal secretion. Ca2+-stimulated amylase secretion was decreased about 50% by metabolic inhibition, while the enhancement by cAMP, TPA or GTP[gamma-S] was totally blocked by metabolic inhibitors. These data demonstrate that amylase secretion in the acinar cell is mediated by multiple intracellular pathways which act in parallel and probably converge at a distal step in the exocytotic process.