V.1. Gastrin-releasing peptide receptor activation: role of cAMP. GRP-R activation results in both increases in cAMP and phospholipase C (PLC). The mGRP-R stably transfected into BALB-3T3 cells behaved in an identical fashion to the wild type on Swiss 3T3 cells, for binding, G-protein coupling, PLC activation and receptor modulation (internalization, down- regulation, desensitization), however it did not cause increases in cAMP, growth or c-fos mRNA. Detailed studies of both cell types demonstrate increases in cAMP do not mediate GRP-R modulation, but are important in bombesin-induced growth. V.2. Role of calcium in pepsinogen secretion. To define the roles of [Ca2+] in pepsinogen release, the effects of thapsigargin, CCK and secretin were compared in dispersed chief cells. Our results demonstrate that: 1) increases in [Ca2+]i due to Ca2+ influx caused by TG or CCK-8 can result in pepsinogen secretion. 2) mobilization of Ca2+ from intracellular sources is important in the rapid initial phase of pepsinogen secretion caused by CCK-8 and 3) the increase in [Ca2] per se whether caused by mobilization from [Ca2+]i stores or Ca2+ influx, is responsible for CCK-8 or TG potentiating secretin-stimulated pepsinogen release. V.3. Action of somatostatin (SS) on chief cells. We demonstrated for the first time that chief cells possess high affinity SS receptors likely of the SSTR/l subtype by binding studies. SS receptor occupation was regulated by agents that activate PKC or adenylate cyclase. SS receptor activation decreased the activity of adenylate cyclase but had no effect on pepsinogen release by various secretagogues. V.4. Distinguishing multiple CCK receptor subtypes. Using dispersed guinea pig chief cells and COS-7 cells transiently transfected with human hCCK/A-R or hCCK/B-R, recently described CCK receptor subtype selective agonists and antagonists are demonstrated to be useful in both species for distinguishing the role of each CCK receptor subtype in different physiological processes. V.5. Subtype of CCK receptor mediating CCK-induced pancreatic growth. CCK stimulates carcinogen-induced tumor formation and growth of the pancreas. In collaboration with Drs. R.H. Bell, Univ. of Cincinnati, and D.S. Longnecker, Dartmouth Medical School, the question of which subtype of CCK receptor mediated these effects was addressed. The results demonstrate CCK interaction with CCK/A receptors, not CCK/B receptors, mediate this pancreatic growth effect in vivo.
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