Dietary and hormonal stimulation of rat exocrine pancreatic function regulates CRHSP-28 phosphorylation in vivo1,2

Dietary regulation of digestive enzyme secretion from the pancreas is essential for the breakdown of macronutrients in the gastrointestinal tract. Ca^sup 2+^-responsive heat stable protein (CRHSP)-28 is a regulatory protein that modulates the exocytosis of digestive enzymes from pancreatic acinar cells. In the present study, isoelectric focusing and immunoblotting were used to characterize CRHSP-28 phosphorylation in isolated rat acinar cells and also after hormonal and dietary stimulation of rat pancreas in vivo. CRHSP-28 was highly phosphorylated in isolated acini after stimulation with a physiologic range of concentrations of cholecystokinin-octapeptide (CCK-8). Activation of the high affinity state of the CCK-A receptor with the synthetic peptide JMV-180 confirmed the physiologic relevance of the response. CRHSP-28 phosphorylation was contingent on elevated cellular Ca^sup 2+^ because it was maximally stimulated by Ca^sup 2+^ ionophore, but unchanged after protein kinase C, cAMP or cyclic guanosine monophosphate activation. Intravenous infusion of rats with a secretory concentration of the CCK analog, caerulein, stimulated CRHSP-28 phosphorylation by 100% over control (P < 0.01) within 15 min of dosing. Moreover, CRHSP-28 phosphorylation was stimulated by 150% over control (P < 0.05) immediately after consumption of a semipurified AIN-93 diet. These data demonstrate that CRHSP-28 phosphorylation occurs in vivo and can be used as a functional indicator of nutrient-driven acinar cell activation. J. Nutr. 133: 3072-3075, 2003. [PUBLICATION ABSTRACT] KEY WORDS: * exocrine pancreas * phosphorylation * CRHSP-28 * secretion * Ca^sup 2+^ -signaling