Amylase secretion from saponin-permeabilized parotid cells evoked by cyclic AMP

Adenosine 3',5'-monophosphate (cAMP) evoked amylase release from saponin-permeabilized parotid cells of the rat. Saponin concentration was optimal at 10 micrograms/ml. Amylase release was stimulated by cAMP almost as well in Ca2+-free medium containing 1 mM EGTA as in the medium containing a physiological concentration of calcium. Although the basal and stimulated releases of amylase were markedly reduced by the further addition of 5 mM EGTA, the effect of cAMP was still detectable. The half-maximal dose of cAMP was 0.3 mM, whereas those of dibutyryl cAMP and 8-bromo-cAMP were 10-fold lower than that of cAMP. In the presence of 10 microM 3-isobutyl-1-methylxanthine, the half-maximal dose of cAMP was also decreased by 5-fold. These results suggest: 1) intracellular calcium is not essential for the exocytosis of amylase stimulated by cAMP; 2) the responsiveness of the cells to exogenous cAMP is reduced by phosphodiesterase.