Regulation of pancreatic protein synthesis by cholecystokinin and calcium

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Abstract
The effect of cholecystokinin (CCK) on [3H]phenylalanine and [14C]tyrosine incorporation into protein was studied in isolated rat pancreatic acini. CCK8, the biologically active octapeptide of CCK, had a biphasic effect on amino acid incorporation. The magnitude of the stimulatory effect (maximal at 10-10-3 .times. 10-10 M CCK8) was greater in diabetic rats, whereas the magnitude of the inhibitory effect (maximal at 10-8 M CCK8) was greater in normal rats. Omission of extracellular Ca2+ from the incubation media did not diminish the stimulatory action of CCK8. Addition of 10-4 M EGTA[ethylene glycol-bis(.beta.-amino ethylether)N,N,N'',N''-tetraacetic acid] to media containing no added Ca2+ lowered basal incorporation, abolished CCK stimulatory effect, and enhanced its inhibitory effect. Stimulation was restored in the presence of Ca2+. The stimulatory effect of the cholinergic analog carbachol (10-5 M) on amino acid incorporation was also abolished by removal of extracellular Ca2+, whereas the stimulatory effect of insulin (1.67 .times. 10-8 M) remained intact. Evidently, CCK and other pancreatic secretagogues enhance pancreatic protein synthesis via Ca2+, whereas stimulation by insulin occurs via another mechanism.

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