Glucose-induced insulin secretion from purified beta-cells. A role for modulation of Ca2+ influx by cAMP- and protein kinase C-dependent signal transduction pathways.
The effects of activation of cAMP- and protein kinase C-dependent signal transduction pathways were investigated on intracellular Ca2+ concentration ([Ca2+]i), cAMP content and insulin secretion from beta-cells purified by fluorescence-activated cell sorting from normal rat islets. The secretion of insulin from suspensions of purified beta-cells was dependent on glucose concentration and hormonal signals, including cAMP and activators of protein kinase C. Microfluorimetric measurement of [Ca2+]i with the fluorescent Ca2+ indicator fura-2 indicated that beta-cells differed immensely in their individual responsiveness to glucose stimulation. An increase in [Ca2+]i occurred in approximately 70% of beta-cells, whereas approximately 30% of beta-cells were nonresponsive to a glucose stimulus. Elevation of cAMP levels by theophylline or glucagon transformed nonresponsive beta-cells into cells which displayed marked increases in [Ca2+]i, and beta-cells which exhibited glucose-induced changes in [Ca2+]i showed further increases in [Ca2+]i and in the amplitude of Ca2+ oscillations. Carbachol and 12-O-tetradecanoylphorbol-13-acetate, activators of protein kinase C, did not induce any alterations in intracellular cAMP levels; nonetheless, these agents increased both the number of beta-cells which exhibited glucose-induced changes in [Ca2+]i and the amplitude of oscillations. The ability of cAMP or activators of protein kinase C to increase [Ca2+]i in single beta-cells was directly correlated with the ability of beta-cell suspensions to secrete insulin in response to a glucose stimulus. These results suggest that both cAMP- and protein kinase C-dependent pathways may regulate Ca2+ entry into beta-cells, possibly via voltage-dependent Ca2+ channels. Thus, this may represent a common mechanism whereby these different signal transduction pathways potentiate glucose-induced insulin secretion from beta-cells.
Wang
J L
JL
Department of Pathology, Washington University School of Medicine, Saint Louis, Missouri 63110.
Corbett
J A
JA
Marshall
C A
CA
McDaniel
M L
ML
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism / Q000502:physiology*; D005934:Glucagon / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013806:Theophylline / Q000494:pharmacology; D013997:Time Factors
D007328:Insulin; D002217:Carbachol; D005934:Glucagon; D013806:Theophylline; D000242:Cyclic AMP; D011493:Protein Kinase C; D005947:Glucose; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium