A NEWLY RECOGNIZED ACTION OF CHOLECYSTOKININ ON PANCREATIC ACINI-RELEASE OF LACTATE-DEHYDROGENASE

In the course of examining the actions of the cholecystokinin octapeptide (CCK-8) on pancreatic acini we found that CCK-8 can stimulate release of the large-molecular-weight cytoplasmic protein, lactate dehydrogenase (LDH) by as much as 6-fold. CCK-8-stimulated LDH release is mediated by a CCK-preferring receptor, detectable at 100 pM CCK-8, maximal at 100 nM CCK-8, constant for up to 30 min, reversible, not desensitized, and dependent on oxidative metabolism and incubation temperature but not on calcium in the extracellular medium. This action of CCK-8 is blocked by inhibitors of protein kinases, staurosporine, H-7, H-8 and H-9, but not by calmodulin antagonists, chlorpromazine, trifluoperazine or W-7. This action of CCK-8 on LDH release is not reproduced by TPA, 8Br-cAMP or A23187. Thus, it appears to be mediated by a previously uncharacterized protein kinase or an isoform of protein kinase C that is not maximally stimulated by TPA.