Regulation of Orai/STIM Channels by pH

This chapter explores the essential methods required to investigate the influence of pH on Orai/STIM channel function as well as molecular mechanisms of pH regulation and highlight future directions in this exciting research field. Since Orai/STIM channels are highly Ca²⁺selective, regulation of channel activity can also be evaluated by directly measuring Ca²⁺influx. The effects of internal pH on Orai/STIM channel activity can also be assessed by the Ca²⁺imaging approach, as conventional patch-clamp can only test one pHi value in a cell. Store depletion can be induced by thapsigargin, a sarcoplasmic/endoplasmic reticulum calcium ATPase pump inhibitor. To understand the mechanism by which external protons regulate Orai/STIM channel activities, mutations of candidate amino acid residues were generated by site-directed mutagenesis. the results of pH regulation of Orai/STIM channels point toward the importance of exploring the therapeutic potential of manipulating I_{Ca²⁺ release–activated} in reverting or preventing pathological consequences of acidosis and alkalosis, such as immunodeficiency and tumor progression.