Store-Operated Ca²⁺ Entry

Abstract

Store-operated Ca²⁺ entry (SOCE) is an ubiquitous and major mechanism for Ca²⁺ influx in mammalian cells with important physiological relevance. Since the discovery of SOCE in 1986 both, the mechanism that communicates the amount of Ca²⁺ accumulated in the intracellular Ca²⁺ stores to the plasma membrane channels and the nature of the capacitative channels, have been a matter of intense investigation. During the last decade, two of the major elements of SOCE, STIM1, the Ca²⁺ sensor of the intracellular Ca²⁺ compartments, and Orai1, the protein forming the channel that conducts the capacitative Ca²⁺ release-activated current I _CRAC, were identified. Together with these proteins, different homologues, including STIM2, Orai2 and Orai3, were identified, although their relevance in SOCE has not been fully characterized yet. Before the identification of STIM1 and Orai1, TRPC proteins were found to be involved in SOCE in different cell types, more likely conducting the non-selective capacitative current described as I _SOC. Current evidence indicates that STIM1, Orai1 and TRPC proteins dynamically interact forming a ternary complex that mediates SOCE in a number of cellular models. The dynamic interaction of STIM1 with Orai1, TRPCs or both might provide an explanation to the distinct capacitative currents described in different cell types.