Komatsu M, McDermott A M, Gillison S L, Sharp G W
Department of Pharmacology, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853.
J Biol Chem. 1993 Nov 5;268(31):23297-306.
Mastoparan, a tetradecapeptide from wasp venom, stimulated exocytosis in a concentration-dependent manner, which was enhanced by pertussis toxin pre-treatment, in the insulin secreting beta-cell line RINm5F. Mastoparan (3-20 microM) also elevated cytosolic free calcium concentration ([Ca2+]i), a rise that was not attenuated by nitrendipine. Divalent cation-free Krebs-Ringer bicarbonate (KRB) medium with 0.1 mM EGTA nullified the mastoparan-induced increase in [Ca2+]i, suggesting that the peptide increased Ca2+ influx but not through the L-type voltage-dependent Ca2+ channel. Depletion of the intracellular Ca2+ pool did not affect the mastoparan-induced elevation of [Ca2+]i. Remarkably, in divalent cation-free KRB medium with 0.1 mM EGTA and 2 microM thapsigargin in which mastoparan reduced [Ca2+]i, the mastoparan-stimulated insulin release was similar to that in normal Ca(2+)-containing KRB medium. Inhibitors of protein kinase C, such as bisindolylmaleimide, staurosporine, and 1-O-hexadecyl-2-O-methyl-rac-glycerol did not suppress the mastoparan-stimulated insulin release. Mastoparan at 10-20 microM did not increase cellular cAMP levels, nor did mastoparan at 5-10 microM affect [3H]arachidonic acid release. In conclusion, although mastoparan increased [Ca2+]i, this increase was not involved in the stimulation of insulin release. Rather, the data suggest that mastoparan directly stimulates exocytosis in a Ca(2+)-independent manner. As GTP-binding proteins (G proteins) are thought to be involved in the process of exocytosis and as mastoparan is known to exert at least some of its effects by activation of G proteins, an action of mastoparan to activate the putative stimulatory Ge (exocytosis) protein is likely.
蜂毒肽是一种来自黄蜂毒液的十四肽，它能以浓度依赖的方式刺激胰岛素分泌β细胞系RINm5F中的胞吐作用，百日咳毒素预处理可增强这种作用。蜂毒肽（3 - 20微摩尔）还能提高胞质游离钙浓度（[Ca2+]i），尼群地平不能减弱这种升高。含有0.1毫摩尔乙二醇双四乙酸（EGTA）的无二价阳离子的克氏-林格碳酸氢盐（KRB）培养基消除了蜂毒肽诱导的[Ca2+]i升高，这表明该肽增加了Ca2+内流，但不是通过L型电压依赖性Ca2+通道。细胞内钙库的耗尽并不影响蜂毒肽诱导的[Ca2+]i升高。值得注意的是，在含有0.1毫摩尔EGTA和2微摩尔毒胡萝卜素的无二价阳离子的KRB培养基中，蜂毒肽降低了[Ca2+]i，但蜂毒肽刺激的胰岛素释放与正常含Ca(2+)的KRB培养基中的相似。蛋白激酶C抑制剂，如双吲哚马来酰胺、星形孢菌素和1 - O - 十六烷基 - 2 - O - 甲基 - rac - 甘油，并不抑制蜂毒肽刺激的胰岛素释放。10 - 20微摩尔的蜂毒肽不会增加细胞内cAMP水平，5 - 10微摩尔的蜂毒肽也不会影响[3H]花生四烯酸的释放。总之，尽管蜂毒肽增加了[Ca2+]i，但这种增加与胰岛素释放的刺激无关。相反，数据表明蜂毒肽以不依赖Ca(2+)的方式直接刺激胞吐作用。由于GTP结合蛋白（G蛋白）被认为参与胞吐过程，且已知蜂毒肽至少部分作用是通过激活G蛋白发挥的，所以蜂毒肽很可能通过激活假定的刺激性Ge（胞吐）蛋白发挥作用。
