钙离子非依赖性磷脂酶A2对大鼠胰岛中胆囊收缩素-8的促胰岛素作用有贡献：与卡巴胆碱的作用机制相分离。

Ca2+-independent phospholipase A2 contributes to the insulinotropic action of cholecystokinin-8 in rat islets: dissociation from the mechanism of carbachol.

作者信息

Simonsson E, Karlsson S, Ahrén B

机构信息

Department of Medicine, Lund University, Malmö, Sweden.

出版信息

Diabetes. 1998 Sep;47(9):1436-43. doi: 10.2337/diabetes.47.9.1436.

DOI:10.2337/diabetes.47.9.1436

PMID:9726232

Abstract

Insulin secretion induced by cholecystokinin-8 (CCK-8) was recently suggested to involve phospholipase A2 (PLA2) activation. In this study, we examined whether CCK-8 stimulates the Ca2+-independent form of PLA2 in isolated rat islets, in comparison with stimulation by the PLA2-activating cholinergic agonist carbachol. We found that CCK-8 (100 nmol/l; 5.6 mmol/l glucose) induces lysophosphatidylcholine accumulation from [3H]palmitate-prelabeled islets (170 +/- 39%; P = 0.003) as well as arachidonic acid (AA) efflux from [3H]AA-prelabeled islets (190 +/- 13%; P < 0.001), and that p-amylcinnamoylantranilic acid (ACA) (50 micromol/l)-mediated PLA2 inhibition reduces CCK-8-induced AA efflux (52 +/- 11%; P = 0.001) and insulin secretion (67 +/- 16%; P < 0.001). Neither the Ca2+ channel antagonist verapamil (100 micromol/l) nor the Ca2+ATPase inhibitor thapsigargin (1 micromol/l) affected CCK-8-induced AA efflux and insulin secretion. Furthermore, despite removal of extracellular Ca2+, CCK-8 still increased AA efflux (48 +/- 14%; P = 0.006) and insulin secretion (105 +/- 46%; P = 0.025). In contrast, carbachol (100 micromol/l)-stimulated AA efflux was reduced by verapamil by 36 +/- 6% (P < 0.001) and abolished by removal of extracellular Ca2+. Overnight protein kinase C (PKC) downregulation by 12-O-tetradecanoyl phorbol-13-acetate (TPA) (500 nmol/l) reduced CCK-8-induced AA efflux (45 +/- 12%; P = 0.003) and insulin secretion (40 +/- 16%; P = 0.020). No additive action regarding either AA formation or insulin secretion was seen by combining TPA overnight and ACA, which implies the involvement of an additional PLA2- and PKC-independent signaling mechanism. The results show that CCK-8, in contrast to carbachol, activates Ca2+-independent PLA2 in islets and that the PLA2-activating capacity of CCK-8 is partly PKC dependent. Hence, Ca2+-independent PLA2 seems important for the insulinotropic effect of CCK-8, but not for that of carbachol.

摘要

最近有研究表明，胆囊收缩素 - 8（CCK - 8）诱导的胰岛素分泌涉及磷脂酶A2（PLA2）的激活。在本研究中，我们检测了CCK - 8是否能刺激分离的大鼠胰岛中不依赖钙离子的PLA2形式，同时与能激活PLA2的胆碱能激动剂卡巴胆碱的刺激作用进行比较。我们发现，CCK - 8（100 nmol/l；5.6 mmol/l葡萄糖）能诱导[3H]棕榈酸预标记的胰岛中溶血磷脂酰胆碱的积累（170±39%；P = 0.003）以及[3H]花生四烯酸（AA）预标记的胰岛中花生四烯酸的流出（190±13%；P < 0.001），并且对氨基肉桂酰邻氨基苯甲酸（ACA）（50 μmol/l）介导的PLA2抑制作用可降低CCK - 8诱导的AA流出（52±11%；P = 0.001）和胰岛素分泌（67±16%；P < 0.001）。钙离子通道拮抗剂维拉帕米（100 μmol/l）和钙离子ATP酶抑制剂毒胡萝卜素（1 μmol/l）均不影响CCK - 8诱导的AA流出和胰岛素分泌。此外，尽管去除了细胞外钙离子，CCK - 8仍能增加AA流出（48±14%；P = 0.006）和胰岛素分泌（105±46%；P = 0.025）。相比之下，卡巴胆碱（100 μmol/l）刺激的AA流出可被维拉帕米降低36±6%（P < 0.001），且在去除细胞外钙离子后被消除。用12 - O - 十四烷酰佛波醇 - 13 - 乙酸酯（TPA）（500 nmol/l）使蛋白激酶C（PKC）过夜下调可降低CCK - 8诱导的AA流出（45±12%；P = 0.003）和胰岛素分泌（40±16%；P = 0.020）。将TPA过夜处理与ACA联合使用时，在AA生成或胰岛素分泌方面未观察到相加作用，这意味着存在一种额外的不依赖PLA2和PKC的信号传导机制。结果表明，与卡巴胆碱不同，CCK - 8能激活胰岛中不依赖钙离子的PLA2形式，且CCK - 8激活PLA2的能力部分依赖于PKC。因此，不依赖钙离子的PLA2似乎对CCK - 8的促胰岛素作用很重要，但对卡巴胆碱的促胰岛素作用不重要。