Effects of phorbol ester and related compounds on acetylcholine-evoked [3H]leucine-labelled protein secretion in permeabilized rat pancreatic acini.
The effects of the phorbol ester, 12-tetradecanoyl-phorbol-13-acetate (TPA) and related compounds on acetylcholine (ACh)-evoked [3H]leucine-labelled protein release (secretion) were tested in isolated permeabilized rat pancreatic acini. The aim was to determine whether the diacylglycerol-like compounds can still potentiate the actions of ACh during unfluctuating supramaximal elevation of cytosolic free calcium (Ca2+) levels. TPA and R59022, an inhibitor of diacylglycerol kinase, evoked marked biphasic dose-dependent increases in 3H-labelled protein secretion from permeabilized rat pancreatic acini. Synthetic diacylglycerol (OAG) and 8-bromo cyclic GMP elicited small increases in 3H-labelled protein release while an inactive phorbol ester (4 alpha-phorbol-12,13-didecanoate; 4 alpha-PDD) and polymyxin B, an inhibitor of protein kinase C, were unable to stimulate secretion. Combining polymyxin B with TPA resulted in an inhibition of 3H-labelled protein secretion. Acetylcholine also induced a dose-dependent increase in 3H-labelled protein output, but when TPA or R59022 was combined with ACh, there was a marked potentiation of the ACh-evoked secretory response, particularly at higher concentrations of ACh. This synergism was unaffected by the protein kinase C inhibitor, polymyxin B. The results show that cytosolic free Ca2+ and protein kinase C may not be the only mediators of ACh-evoked secretion. Moreover, they indicate that protein kinase C may not be involved in the potentiation by TPA of ACh-evoked 3H-labelled protein release.
Francis
L P
LP
School of Applied Biology, Lancashire Polytechnic, Preston, Lancs.
Singh
J
J
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000187:drug effects; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000378:metabolism; D008297:Male; D010179:Pancreas / Q000187:drug effects* / Q000378:metabolism; D010742:Phospholipid Ethers / Q000494:pharmacology; D011112:Polymyxin B / Q000494:pharmacology; D011506:Proteins / Q000378:metabolism*; D011744:Pyrimidinones / Q000494:pharmacology; D051381:Rats; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D013844:Thiazoles / Q000494:pharmacology
D007295:Inositol Phosphates; D010742:Phospholipid Ethers; D011506:Proteins; D011744:Pyrimidinones; D013844:Thiazoles; C057178:1-O-octadecyl-2-azelaorylglycerophosphocholine; C016276:8-bromocyclic GMP; C047505:R 59022; D006152:Cyclic GMP; D011112:Polymyxin B; D000109:Acetylcholine; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium