Beauvois Melanie C, Arredouani Abdelilah, Jonas Jean-Christophe, Rolland Jean-François, Schuit Frans, Henquin Jean-Claude, Gilon Patrick
Unité d'Endocrinologie et Métabolisme, University of Louvain Faculty of Medicine, Brussels, Belgium.
J Physiol. 2004 Aug 15;559(Pt 1):141-56. doi: 10.1113/jphysiol.2004.067454. Epub 2004 Jun 24.
The contribution of Ca(2+) release from intracellular stores to the rise in the free cytosolic Ca(2+) concentration (Ca(2+)) triggered by Ca(2+) influx was investigated in mouse pancreatic beta-cells. Depolarization of beta-cells by 45 mm K(+) (in the presence of 15 mm glucose and 0.1 mm diazoxide) evoked two types of Ca(2+) responses: a monotonic and sustained elevation; or a sustained elevation superimposed by a transient Ca(2+) peak (TCP) (40-120 s after the onset of depolarization). Simultaneous measurements of Ca(2+) and voltage-dependent Ca(2+) current established that the TCP did not result from a larger Ca(2+) current. Abolition of the TCP by thapsigargin and its absence in sarco-endoplasmic reticulum Ca(2+)-ATPase 3 (SERCA3) knockout mice show that it is caused by Ca(2+) mobilization from the endoplasmic reticulum. A TCP could not be evoked by the sole depolarization of beta-cells but required a rise in Ca(2+) pointing to a Ca(2+)-induced Ca(2+) release (CICR). This CICR did not involve inositol 1,4,5-trisphosphate (IP(3)) receptors (IP(3)Rs) because it was resistant to heparin. Nor did it involve ryanodine receptors (RyRs) because it persisted after blockade of RyRs with ryanodine, and was not mimicked by caffeine, a RyR agonist. Moreover, RyR1 and RyR2 mRNA were not found and RyR3 mRNA was only slightly expressed in purified beta-cells. A CICR could also be detected in a limited number of cells in response to glucose. Our data demonstrate, for the first time in living cells, the existence of an atypical CICR that is independent from the IP(3)R and the RyR. This CICR is prominent in response to a supraphysiological stimulation with high K(+), but plays little role in response to glucose in non-obese mouse pancreatic beta-cells.
在小鼠胰腺β细胞中，研究了细胞内钙库释放的Ca(2+)对由Ca(2+)内流引发的胞质游离Ca(2+)浓度（[Ca(2+)]c）升高的贡献。用45 mM K(+)使β细胞去极化（在存在15 mM葡萄糖和0.1 mM二氮嗪的情况下）引发了两种类型的[Ca(2+)]c反应：一种单调且持续的升高；或一种持续升高并叠加有瞬时[Ca(2+)]c峰值（TCP）（去极化开始后40 - 120秒）。同时测量[Ca(2+)]c和电压依赖性Ca(2+)电流表明，TCP并非由更大的Ca(2+)电流引起。毒胡萝卜素消除了TCP，且在肌浆内质网Ca(2+)-ATP酶3（SERCA3）基因敲除小鼠中不存在TCP，这表明它是由内质网释放Ca(2+)引起的。仅β细胞去极化不能诱发TCP，而是需要[Ca(2+)]c升高，这表明是钙诱导的钙释放（CICR）。这种CICR不涉及肌醇1,4,5-三磷酸（IP(3)）受体（IP(3)Rs），因为它对肝素具有抗性。它也不涉及兰尼碱受体（RyRs），因为在用兰尼碱阻断RyRs后它仍然存在，并且未被RyR激动剂咖啡因模拟。此外，在纯化的β细胞中未发现RyR1和RyR2 mRNA，RyR3 mRNA仅轻微表达。在有限数量的细胞中，对葡萄糖的反应也可检测到CICR。我们的数据首次在活细胞中证明了存在一种独立于IP(3)R和RyR的非典型CICR。这种CICR在对高K(+)的超生理刺激反应中很突出，但在非肥胖小鼠胰腺β细胞对葡萄糖的反应中作用很小。
