Effects of protein kinase C activation on the regulation of the stimulus-secretion coupling in pancreatic beta-cells.
Effects of protein kinase C (PKC) activation on the insulin-secretory process were investigated, by using beta-cell-rich suspensions obtained from pancreatic islets of obese-hyperglycaemic mice. The phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA), which is known to activate PKC directly, the muscarinic-receptor agonist carbamoylcholine and high glucose concentration enhanced the phosphorylation of a specific 80 kDa PKC substrate in the beta-cells. At a non-stimulatory glucose concentration, 10 nM-TPA increased insulin release, although there were no changes in either the cytoplasmic free Ca2+ concentration ([Ca2+]i) or membrane potential, as measured with the fluorescent indicators quin-2 and bisoxonol respectively. At a stimulatory glucose concentration TPA caused a lowering in [Ca2+]i, whereas membrane potential was unaffected. Despite the decrease in [Ca2+]i, there was a large stimulation of insulin release. Addition of TPA lowered [Ca2+]i also in beta-cells stimulated by tolbutamide or high K+, although to a lesser extent than in those stimulated by glucose. There was no effect of TPA on either Ca2+ buffering or the ability of Ins(1,4,5)P3 to release Ca2+ in permeabilized beta-cells. However, the phorbol ester inhibited the rise in [Ca2+]i in response to carbamoylcholine, which stimulates the formation of InsP3, in intact beta-cells. Down-regulation of PKC influenced neither glucose-induced insulin release nor the increase in [Ca2+]i. Hence, although PKC activation is of no major importance in glucose-stimulated insulin release, this enzyme can serve as a modulator of the glucose-induced insulin-secretory response. Such a modulation involves mechanisms promoting both amplification of the secretory response and lowering of [Ca2+]i.
Arkhammar
P
P
Department of Medical Cell Biology, Uppsala University, Sweden.
Nilsson
T
T
Welsh
M
M
Welsh
N
N
Berggren
P O
PO
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D003593:Cytoplasm / Q000378:metabolism; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D004224:Diterpenes; D004789:Enzyme Activation; D005711:Gallopamil / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects*; D051379:Mice; D008820:Mice, Obese; D010750:Phosphoproteins / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D011493:Protein Kinase C / Q000502:physiology*; D013729:Terpenes / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014044:Tolbutamide / Q000494:pharmacology
D004224:Diterpenes; D007328:Insulin; D010750:Phosphoproteins; D013729:Terpenes; C011309:mezerein; D005711:Gallopamil; D002217:Carbachol; D014044:Tolbutamide; D011493:Protein Kinase C; D005947:Glucose; D013755:Tetradecanoylphorbol Acetate; D011188:Potassium; D002118:Calcium; D004121:Dimethyl Sulfoxide