Regulation of endogenous and heterologous Ca2+ release-activated Ca2+ currents by pH

Deviations from physiological pH (similar to pH 7.2) as well as altered Ca2+ signaling play important roles in immune disease and cancer. One of the most ubiquitous pathways for cellular Ca2+ influx is the store-operated Ca2+ entry (SOCE) or Ca2+ release-activated Ca2+ current (I-CRAC), which is activated upon depletion of intracellular Ca2+ stores. We here show that extracellular and intracellular changes in pH regulate both endogenous I-CRAC in Jurkat T lymphocytes and RBL2H3 cells, and heterologous I-CRAC in HEK293 cells expressing the molecular components STIM1/2 and Orai1/2/3 (CRACM1/2/3). We find that external acidification suppresses, and alkalization facilitates IP3-induced I-CRAC. In the absence of IP3, external alkalization did not elicit endogenous lam but was able to activate heterologous I-CRAC in HEK293 cells expressing Orai1/2/3 and STIM1 or STIM2. Similarly, internal acidification reduced IP3-induced activation of endogenous and heterologous I-CRAC, while alkalization accelerated its activation kinetics without affecting overall current amplitudes. Mutation of two aspartate residues to uncharged alanine amino acids (D110/112A) in the first extracellular loop of Orai1 significantly attenuated both the inhibition of low by external acidic pH as well as its facilitation by alkaline conditions. We conclude that intra- and extracellular pH differentially regulates I-CRAC. While intracellular pH might affect aggregation and/or binding of STIM to Orai, external pH seems to modulate I-CRAC through its channel pore, which in Orai1 is partially mediated by residues D110 and D112. (C) 2014 Elsevier Ltd. All rights reserved.