Arkhammar P, Nilsson T, Welsh M, Welsh N, Berggren P O
Department of Medical Cell Biology, Uppsala University, Sweden.
Biochem J. 1989 Nov 15;264(1):207-15. doi: 10.1042/bj2640207.
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.
利用从肥胖高血糖小鼠胰岛中获得的富含β细胞的悬液，研究了蛋白激酶C（PKC）激活对胰岛素分泌过程的影响。佛波酯12 - O - 十四烷酰佛波醇13 - 乙酸酯（TPA）已知可直接激活PKC，毒蕈碱受体激动剂卡巴胆碱和高葡萄糖浓度可增强β细胞中一种特定的80 kDa PKC底物的磷酸化。在非刺激性葡萄糖浓度下，10 nM - TPA增加了胰岛素释放，尽管分别用荧光指示剂喹-2和双苯磺酰草胺测量时，细胞质游离Ca2+浓度（[Ca2+]i）和膜电位均无变化。在刺激性葡萄糖浓度下，TPA导致[Ca2+]i降低，而膜电位未受影响。尽管[Ca2+]i降低，但胰岛素释放仍受到很大刺激。TPA的添加也降低了甲苯磺丁脲或高钾刺激的β细胞中的[Ca2+]i，尽管程度小于葡萄糖刺激的细胞。TPA对通透化β细胞中的Ca2+缓冲或Ins(1,4,5)P3释放Ca2+的能力均无影响。然而，在完整的β细胞中，佛波酯抑制了对卡巴胆碱的[Ca2+]i升高反应，卡巴胆碱刺激InsP3的形成。PKC的下调既不影响葡萄糖诱导的胰岛素释放，也不影响[Ca2+]i的增加。因此，尽管PKC激活在葡萄糖刺激的胰岛素释放中并非至关重要，但该酶可作为葡萄糖诱导的胰岛素分泌反应的调节剂。这种调节涉及促进分泌反应放大和降低[Ca2+]i的机制。
