AJP - Gastrointestinal and Liver Physiology, Vol 246, Issue 5 500-G508, Copyright © 1984 by American Physiological Society
Activation of protein kinase activity in pancreatic acini by calcium and cAMP
D. B. Burnham and J. A. Williams
Regulation of protein kinase activity by calcium and cAMP was investigated
in cytosolic and particulate preparations from isolated mouse pancreatic
acini. In cytosol, three protein kinase activities could be distinguished:
a calcium-activated kinase activity that was increased by exogenous
calmodulin (CaM) and abolished by treatment of cytosol with a
phenothiazine-coupled resin, a calcium-activated kinase activity dependent
on phosphatidylserine (PS), and cAMP-activated kinase activity.
Phosphorylation of a Mr = 92,000 cytosolic protein was greatly increased by
both CaM-dependent and cAMP-activated kinases, whereas PS-dependent kinase
activity most heavily phosphorylated proteins of Mr = 62,000 and 40,000. In
addition, these kinase activities demonstrated differences in specificity
for exogenous protein substrates. CaM-and PS-dependent kinases were
completely blocked by trifluoperazine; the inhibitor protein of
cAMP-activated protein kinase selectively inhibited cAMP-activated kinase
activity. Exogenous CaM decreased the concentration of free calcium for
half-maximal activation of CaM-dependent kinase activity from 5.5 +/- 0.5
to 1.2 +/- 0.3 microM Ca2+; half-maximal activation of the PS-dependent and
cAMP-activated kinase activities was achieved at 12 microM Ca2+ and 40-50
nM cAMP, respectively. In a particulate fraction depleted of endogenous
CaM, CaM-dependent and cAMP-activated kinase activities were detected. In
conclusion, this study demonstrates the existence of protein kinases in
pancreatic acini which may be involved in the action of pancreatic
regulatory agents that use calcium or cAMP as an intracellular messenger.
