Store-Operated Ca2+ Entry Mediated by Orai1 and TRPC1 Participates to Insulin Secretion in Rat β-Cells

Abstract

Store-Operated Ca2+ Channels (SOCs) are voltage-independent Ca2+ channels activated upon depletion of the endoplasmic reticulum (ER) Ca2+ stores. Early studies suggest the contribution of such channels to Ca2+ homeostasis in insulin-secreting pancreatic β-cells. However, their composition and contribution to glucose-stimulated insulin secretion (GSIS) remain unclear. In this study, ER Ca2+ depletion triggered by acetylcholine (ACh) or thapsigargin (Tg) stimulated the formation of a ternary complex composed of Orai1, TRPC1 and STIM1, the key proteins involved in the formation of SOCs. Ca2+ imaging further revealed that Orai1 and TRPC1 are required to form functional SOCs and that these channels are activated by STIM1 in response to Tg or ACh. Pharmacological SOCs inhibition or dominant-negative blockade of Orai1 or TRPC1 using the specific pore mutants Orai1-E106D or TRPC1-F562A impaired GSIS in rat β-cells and fully blocked the potentiating effect of ACh on secretion. In contrast, pharmacological or dominant-negative blockade of TRPC3 had no effect on extracellular Ca2+ entry and GSIS. Finally, we observed that prolonged exposure to supraphysiological glucose concentration impaired SOCs function without altering the expression levels of STIM1, Orai1 and TRPC1. We conclude that Orai1 and TRPC1, which form SOCs regulated by STIM1, play a key role in the effect of ACh on GSIS, a process which may be impaired in type 2 diabetes.