Rosengren A, Filipsson K, Jing X-J, Reimer M K, Renström E
Department of Physiological Sciences, Lund University, BMC F11, Tornavägen 10, 221 84 Lund, Sweden.
Pflugers Arch. 2002 Jul;444(4):556-67. doi: 10.1007/s00424-002-0866-1. Epub 2002 Jun 12.
The cAMP-elevating pituitary adenylate cyclase-activating polypeptide (PACAP) stimulates insulin release in pancreatic B-cells. Here, we have investigated its potentiating action in rat insulinoma INS-1 cells. In intact cells, PACAP-27 (100 nM) stimulated glucose-induced insulin secretion by >60%. Using the patch-clamp technique with single-cell exocytosis monitored as increases in cell capacitance, we observed that at 10 mM and 20 mM extracellular glucose, PACAP-27 acted mainly by a >50% enhancement of depolarization-elicited Ca(2+) entry, whereas at low (3 mM) glucose, the predominant effect of the peptide was a twofold increase in Ca(2+) sensitivity of insulin exocytosis. The latter effect was mimicked by glucose itself in a dose-dependent fashion. PACAP-27 exerts a prolonged effect on insulin secretion that is dissociated from changes of cytoplasmic cAMP. Whereas an elevation of cellular cAMP content (135%) could be observed 2 min after addition of PACAP-27, after 30 min preincubation with the peptide, cAMP concentrations were not different from basal. Yet, such pretreatment with PACAP-27 stimulated subsequent insulin release by congruent with60%. This sustained action is likely to reflect an increased degree of protein-kinase-A-dependent phosphorylation, and inhibitors of the kinase largely prevented the PACAP-mediated effects.
可升高环磷酸腺苷（cAMP）的垂体腺苷酸环化酶激活多肽（PACAP）可刺激胰腺β细胞释放胰岛素。在此，我们研究了其对大鼠胰岛素瘤INS-1细胞的增强作用。在完整细胞中，PACAP-27（100 nM）可使葡萄糖诱导的胰岛素分泌增加60%以上。使用膜片钳技术，通过监测单细胞胞吐作用引起的细胞电容增加，我们观察到在细胞外葡萄糖浓度为10 mM和20 mM时，PACAP-27主要通过使去极化引发的Ca(2+)内流增加50%以上来发挥作用，而在低葡萄糖浓度（3 mM）时，该肽的主要作用是使胰岛素胞吐作用的Ca(2+)敏感性增加两倍。后一种作用可被葡萄糖本身以剂量依赖的方式模拟。PACAP-27对胰岛素分泌具有持久作用，且与细胞质cAMP的变化无关。虽然在添加PACAP-27后2分钟可观察到细胞cAMP含量升高（135%），但在与该肽预孵育30分钟后，cAMP浓度与基础水平无差异。然而，这种用PACAP-27进行的预处理可使随后的胰岛素释放增加60%左右。这种持续作用可能反映了蛋白激酶A依赖性磷酸化程度的增加，并且该激酶的抑制剂在很大程度上阻止了PACAP介导的作用。
