Li G, Pralong W F, Pittet D, Mayr G W, Schlegel W, Wollheim C B
Division de Biochimie Clinique, University of Geneva, Switzerland.
J Biol Chem. 1992 Mar 5;267(7):4349-56.
Signal generation during the stimulation of insulin secretion by arginine vasopressin (AVP) was investigated in RINm5F cells. AVP (0.1 microM) caused a biphasic cytosolic Ca2+ ([Ca2+]i) rise, namely a rapid transient marked elevation after stimulation followed by a series of oscillations. In the absence of extracellular Ca2+, the sustained oscillations were abolished, while the initial [Ca2+]i transient was only partly decreased, indicating that the former are due to Ca2+ influx and the latter due mainly to mobilization from internal Ca2+ stores. AVP also evoked a transient depolarization of the average membrane potential. AVP-induced Ca2+ influx during the sustained phase, which was strictly dependent on receptor occupancy, was attenuated by membrane hyperpolarization with diazoxide. However, blockade of Ca2+ channels of the L- or T-type was ineffective. AVP stimulated production of diacylglycerol and inositol phosphates; for the latter both [3H] inositol labeling and mass determinations were performed. A transient increase in Ins(1,4,5)P3 was followed by a marked enhancement of Ins(1,3,4,5)P4 (8-fold) peaking at 15 s and gradually returning to basal values. Ins(1,3,4,6)P4 and Ins(3,4,5,6)P4 exhibited the most long-lasting augmentation (4- and 1.7-fold, respectively), and therefore correlated best with the period of sustained [Ca2+]i oscillations. InsP5 and InsP6 were not elevated. The effects of AVP, including the stimulation of insulin secretion from perifused cells, were obliterated by a V1 receptor antagonist. In conclusion, AVP induces protracted [Ca2+]i elevation in RINm5F cells which is associated with long-lasting increases in InsP4 isomers. The accumulation of InsP4 isomers reflects receptor occupancy and accelerated metabolism of the inositol phosphates. Activation of second messenger-operated Ca2+ channels is not necessarily implicated because of the attenuating effect of membrane hyperpolarization.
在RINm5F细胞中研究了精氨酸加压素（AVP）刺激胰岛素分泌过程中的信号产生情况。AVP（0.1微摩尔）引起胞质Ca2+（[Ca2+]i）双相升高，即刺激后迅速出现短暂的显著升高，随后是一系列振荡。在无细胞外Ca2+的情况下，持续振荡消失，而初始[Ca2+]i瞬变仅部分降低，表明前者是由于Ca2+内流，后者主要是由于从内部Ca2+储存库中释放。AVP还引起平均膜电位的短暂去极化。在持续阶段，AVP诱导的Ca2+内流严格依赖于受体占据情况，用二氮嗪使膜超极化可减弱这种内流。然而，L型或T型Ca2+通道的阻断无效。AVP刺激二酰基甘油和肌醇磷酸的产生；对于后者，进行了[3H]肌醇标记和质量测定。Ins(1,4,5)P3短暂增加后，Ins(1,3,4,5)P4显著增强（8倍），在15秒达到峰值，然后逐渐恢复到基础值。Ins(1,3,4,6)P4和Ins(3,4,5,6)P4表现出最持久的增强（分别为4倍和1.7倍），因此与持续的[Ca+]i振荡期相关性最好。InsP5和InsP6没有升高。V1受体拮抗剂消除了AVP的作用，包括刺激灌流细胞分泌胰岛素。总之，AVP在RINm5F细胞中诱导持久的[Ca2+]i升高，这与InsP4异构体的持久增加有关。InsP4异构体积累反映受体占据情况和肌醇磷酸代谢加速。由于膜超极化的减弱作用，不一定涉及第二信使操作的Ca2+通道的激活。
