Henquin J C, Bozem M, Schmeer W, Nenquin M
Unité de Diabétologie et Nutrition, Faculté de Médecine, Université Catholique de Louvain, Bruxelles.
Biochem J. 1987 Sep 1;246(2):393-9. doi: 10.1042/bj2460393.
The mechanisms whereby activation of the cyclic AMP-dependent protein kinase A or the Ca2+-phospholipid-dependent protein kinase C amplifies insulin release were studied with mouse islets. Forskolin and the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) were used to stimulate adenylate cyclase and protein kinase C respectively. The sulphonylurea tolbutamide was used to initiate insulin release in the presence of 3 mM-glucose. Tolbutamide alone inhibited 86Rb+ efflux, depolarized beta-cell membrane, triggered electrical activity, accelerated 45Ca2+ influx and efflux and stimulated insulin release. Forskolin alone only slightly inhibited 86Rb+ efflux, but markedly increased the effects of tolbutamide on electrical activity, 45Ca2+ influx and efflux, and insulin release. In the absence of Ca2+, only the inhibition of 86Rb+ efflux persisted. TPA (100 nM) alone slightly accelerated 45Ca2+ efflux and insulin release without affecting 45Ca2+ influx or beta-cell membrane potential. It increased the effects of tolbutamide on 45Ca2+ efflux and insulin release without changing 86Rb+ efflux, 45Ca2+ influx or electrical activity. Omission of extracellular Ca2+ suppressed all effects due to the combination of TPA and tolbutamide, but not those of TPA alone. Though ineffective alone, 10 nM-TPA amplified the releasing action of tolbutamide without affecting its ionic and electrical effects. In conclusion, the two amplification systems of insulin release involve at least partially distinct mechanisms. The cyclic AMP but not the protein kinase C system initiating signal (Ca2+ influx) triggered by the primary secretagogue.
利用小鼠胰岛研究了环磷酸腺苷依赖性蛋白激酶A或钙 - 磷脂依赖性蛋白激酶C的激活增强胰岛素释放的机制。分别使用福斯高林和佛波酯12 - O - 十四酰佛波醇13 - 乙酸酯（TPA）刺激腺苷酸环化酶和蛋白激酶C。在存在3 mM葡萄糖的情况下，使用磺脲类药物甲苯磺丁脲引发胰岛素释放。单独使用甲苯磺丁脲可抑制86Rb⁺外流，使β细胞膜去极化，引发电活动，加速45Ca²⁺内流和外流并刺激胰岛素释放。单独使用福斯高林仅轻微抑制86Rb⁺外流，但显著增强甲苯磺丁脲对电活动、45Ca²⁺内流和外流以及胰岛素释放的作用。在无Ca²⁺的情况下，仅86Rb⁺外流的抑制持续存在。单独使用TPA（100 nM）可轻微加速45Ca²⁺外流和胰岛素释放，而不影响45Ca²⁺内流或β细胞膜电位。它增强了甲苯磺丁脲对45Ca²⁺外流和胰岛素释放的作用，而不改变86Rb⁺外流、45Ca²⁺内流或电活动。去除细胞外Ca²⁺可抑制TPA和甲苯磺丁脲联合作用产生的所有效应，但不影响单独TPA的效应。虽然单独无效，但10 nM - TPA增强了甲苯磺丁脲的释放作用，而不影响其离子和电效应。总之，胰岛素释放的两种增强系统至少部分涉及不同的机制。环磷酸腺苷系统而非蛋白激酶C系统引发由主要促分泌剂触发的信号（Ca²⁺内流）。
