Hashiguchi Hiroshi, Nakazaki Mitsuhiro, Koriyama Nobuyuki, Fukudome Michiyo, Aso Katsumi, Tei Chuwa
Department of Cardiovascular, Respiratory and Metabolic Medicine, Kagoshima University, Kagoshima, Japan.
Diabetes Metab Res Rev. 2006 Jan-Feb;22(1):64-71. doi: 10.1002/dmrr.580.
Cyclic AMP (cAMP) plays a pivotal role in insulin secretion induced by incretins. The effects of the second messenger extend to many sites and there has been much controversy on the mechanisms. The aim of this study was to examine how cAMP amplified insulin exocytosis.
Rat islets were permeabilized with alpha-toxin to measure insulin exocytosis in the fixed conditions of Ca(2+) and ATP. The effects of several agents on insulin exocytosis were observed in perifusion experiments.
Cyclic AMP enhanced the Ca(2+)-induced insulin release by around 30%, independent of Ca(2+) concentrations between 10 and 3000 nmol/L. A cAMP-GEF selective cAMP analogue, 8-(4-chloro-phenylthio)-2'-O-methyladenosine-3',5'-cyclic monophosphate, also amplified insulin release. The effect disappeared in the absence of ATP. Conversely, cAMP-independent gradual increase in insulin release was observed with ATP. These results suggested that the site of action of cAMP-GEF existed proximal to that of ATP. An analogue selective to PKA, N(6)-Benzoyladenosine-3',5'-cyclic monophosphate, had little effect. Also, a PKA-selective inhibitor, N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide, reduced insulin releases induced by 1000 nmol/L Ca(2+), but did not influence the relative increase produced by Ca(2+) and cAMP.
Cyclic AMP potentiated Ca(2+) and ATP-induced exocytosis to a similar relative extent independent of Ca(2+) concentrations. The process appeared to be mainly mediated by cAMP-GEF. In addition, the cAMP/cAMP-GEF pathway may enhance insulin release by replenishing the readily releasable pool.
环磷酸腺苷（cAMP）在肠促胰岛素诱导的胰岛素分泌中起关键作用。第二信使的作用延伸至多个位点，其作用机制存在诸多争议。本研究旨在探讨cAMP如何放大胰岛素胞吐作用。
用α - 毒素使大鼠胰岛通透化，以在固定的Ca(2+)和ATP条件下测量胰岛素胞吐作用。在灌流实验中观察几种药物对胰岛素胞吐作用的影响。
cAMP使Ca(2+)诱导的胰岛素释放增强约30%，与10至3000 nmol/L之间的Ca(2+)浓度无关。一种cAMP - GEF选择性cAMP类似物，8 - （4 - 氯苯基硫代） - 2'-O - 甲基腺苷 - 3',5'-环磷酸单酯，也能放大胰岛素释放。在无ATP时该作用消失。相反，ATP可使胰岛素释放出现不依赖cAMP的逐渐增加。这些结果表明cAMP - GEF的作用位点存在于ATP作用位点的近端。一种对蛋白激酶A（PKA）有选择性的类似物，N(6)-苯甲酰腺苷 - 3',5'-环磷酸单酯，作用很小。此外，一种PKA选择性抑制剂，N - [2 - （对溴肉桂酰胺基）乙基] - 5 - 异喹啉磺酰胺，可降低1000 nmol/L Ca(2+)诱导的胰岛素释放，但不影响Ca(2+)和cAMP产生的相对增加。
cAMP在相似的相对程度上增强Ca(2+)和ATP诱导的胞吐作用，与Ca(2+)浓度无关。该过程似乎主要由cAMP - GEF介导。此外，cAMP/cAMP - GEF途径可能通过补充易释放池来增强胰岛素释放。
