Activation of the muscarinic receptor in bovine adrenal medullary chromaffin cells causes a rise in intracellular Ca2+ without stimulating secretion

Table 1 also shows that cyclic AMP concentrations were increased to the same extent by PGE2 and 3-isobutyl-1methyl xanthine, but that PGEz was a much less potent stimulator of mucin release. Thus our results have demonstrated a lack of correlation between magnitude of increase in cyclic AMP concentration and degree of stimulation of mucin secretion. They suggest that increased cyclic AMP concentration alone is not a sufficient trigger for mucin secretion. Our previous studies have shown that although Ca2+ is not a primary trigger of mucin secretion (McPherson & Dormer, 1984a), 0-adrenergic secretagogues increase cell Ca” mobilization (McPherson & Dormer, 19846); whether PGEz has a similar action is not known. In any event, addition of exogenous prostaglandins does not appear to modulate the actions of 0-adrenergic agonists in triggering mucin secretion. In addition, our results (data not shown) indicate that indomethacin M ) , an inhibitor of prostaglandin synthesis, also does not affect isoproterenolstimulation of mucin secretion. This suggests that the observed stimulatory actions of isoproterenol on secretion cannot be attributed to increased synthesis of endogenous prostaglandins. of PGE2. In summary, it is apparent from our results that the acinar cells of the rat submandibular gland respond to prostaglandin Ez in terms of increased cyclic AMP concentration; however, the cellular functions relating to this event remain to be elucidated.