Effect of 12-O-tetradecanoyl-phorbol-13-acetate on Ca2+ efflux and protein discharge in pancreatic acini.
When pancreatic acini are exposed to the peptide caerulein (an analogue of the hormone cholecystokinin) or the cholinergic agonist carbamylcholine, they exhibit a rapid release of intracellular Ca2+ and a rise in the level of cGMP, accompanied by discharge of secretory proteins. The phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) stimulates protein discharge without affecting the level of cGMP, while N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) elevates cGMP, but does not elicit discharge (Gunther, G. R., and Jamieson, J. D. (1979) Nature 280, 318-320). To clarify the relationships among these events, the effect of tPA and MNNG on Ca2+ efflux in guinea pig acini was determined. Cells were incubated in medium containing 45Ca2+ and transferred to medium with nonradioactive Ca2+ before adding the agents to be tested. Caerulein (10(-9) M), carbamylcholine (10(-5) M), and the Ca2+ ionophore A23187 (5 micrograms/ml) all caused the release of 40-60% of the cell-associated 45Ca2+ within 3 min. In contrast, acini incubated with 10(-7) M TPA, 10(-4) M MNNG, or no added agents retained over 80% of their 45Ca2+ after 22 min. TPA caused significant secretory discharge within the first 15 min and did not block CA2+ efflux stimulated by other secretagogues. TPA-induced discharge requires energy and the presence of sufficient Ca2+ in the extracellular medium. These observations are consistent with a model in which the rapid release of Ca2+ into the cytoplasm triggers an increase in the level of cGMP and, by a separate series of events, protein discharge. TPA may act at a later point on the pathway to discharge, but before an obligatory step requiring Ca2+.
D000681:Amylases / Q000378:metabolism; D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002108:Ceruletide / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism; D005260:Female; D006168:Guinea Pigs; D007700:Kinetics; D010179:Pancreas / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010704:Phorbols / Q000494:pharmacology*; D011506:Proteins / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D010704:Phorbols; D011506:Proteins; D000001:Calcimycin; D002108:Ceruletide; D002217:Carbachol; D000242:Cyclic AMP; D000681:Amylases; D006152:Cyclic GMP; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium