Effects of Stimulation of Adenylate Cyclase and Protein Kinase-C on Cultured Fetal Rat B-Cells*

Abstract

To study the maturation of fetal pancreatic B-cells, cell suspensions of pancreas from 21.5-day-old fetuses were cultured in RPMI medium containing 10 mM glucose. Forskolin (1 microM), used to stimulate adenylate cyclase, moderately delayed the neoformation of islets, slightly accelerated the proliferation of endocrine cells, and considerably increased insulin release by the cultures. The latter increase was not completely compensated for by the stimulation of insulin biosynthesis, so that the islet insulin content was decreased. The phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA; 25 nM), used to stimulate protein kinase-C, had little effect on the evolution of the cultures, but increased insulin release. This increase was almost compensated for by the stimulation of insulin biosynthesis. After 9-10 days of culture, insulin release in response to 15 mM glucose or 10 mM leucine was studied with perifused islets. In control islets, glucose produced a sustained increase in insulin release, which, however, was 6-fold smaller than that produced by leucine. Addition of forskolin or TPA to the perifusion medium markedly amplified the response to glucose without causing a biphasic pattern of release. In islets cultured with forskolin, the insulin response to glucose or leucine was decreased, largely owing to the lower insulin stores. In islets cultured with TPA, the insulin response to glucose or leucine was also decreased, but these differences cannot be explained simply by changes in insulin content. Neither treatment affected the kinetics of release. In conclusion, acute stimulation of adenylate cyclase or protein kinase-C markedly increased insulin release from fetal islets without causing an adult-like biphasic pattern of secretion. Chronic stimulation did not accelerate maturation of B-cells.

Modulation of Glucose-Induced Insulin Secretion from a Rat Clonal β-Cell Line*

“…Forskolin increases the cAMP content of neonatal islets, induces an adultlike insulin secretory response to glucose, and shifts the maximal secretory response to higher concentrations of glucose (9). In the present studies forskolin and other cAMP modulators potentiated secretion, but did not alter the glucose sensitivity of RIN-38 cells; similar results were recently reported with fetal islets (34). Similar to fetal islets (but not adult islets 25), RIN-38 cells secrete insulin in response to alanine.…”

Development of the insulin secretion mechanism in fetal and neonatal rat pancreatic B-cells: response to glucose, K+, theophylline, and carbamylcholine

“…In B-cells, the intracellular levels of these second messengers can be increased by the stimulation of adenylylcyclase and phospholipase C, respectively. It is well established that both of these pathways are important modulators of insulin secretion in fetal, neonatal, and adult islets (10,(19)(20)(21). In 19-dayold fetuses, theophylline stimulated insulin secretion, thus confirming that this pathway is already operative at this age and that it is fundamental for insulin secretion during fetal life.…”

Pancreatic Beta-cell growth and diabetes mellitus

“…Investigations are contradictory and difficult to interpret. Stimulation of endogenous cAMP formation with forskolin or glucagon enhances islet cell DNA replication [66,82]. Cyclic AMP analogues have been reported both inhibitory and stimulatory [83,84].…”