Ca 2+ modulation of volume‐regulated anion channels: evidence for colocalization with store‐operated channels

Ca 2+ regulation of Cl − current induced by cell swelling (I Cl , swell ) in response to hypotonicity was studied in human prostate cancer epithelial cells (LNCaP) by using the patch‐clamp technique. Increase of global intracellular Ca 2+ ([Ca 2+ ] in ) to 1 μM as well as variations of the extracellular Ca 2+ ([Ca 2+ ] out ) in the 0 to 10 mM range did not affect time course of the development, maximal amplitude, rectification properties, and kinetics of I Cl,swell . However, the presence of 0.1 μM thapsigargin (TG), an inhibitor of endoplasmic reticulum (ER) Ca 2+ pump, resulted in a more than 50% inhibition of I Cl,swell . The blockade of plasma membrane store‐operated channels (SOCs), activated in the presence of TG, by 2 mM Ni 2+ prevented TG‐conferred I Cl,swell inhibition by extracellular Ca 2+ . In the presence of TG and Ca 2+ , the cells failed to exhibit regulatory volume decrease. We conclude that interaction between volume‐regulated anion channels (VRACs) carrying I Cl,swell and Ca 2+ occurs in the microdomains from the inner surface of the membrane that are not accessible to the changes in [Ca 2+ ]in, but can be readily reached by Ca 2+ entering the cell via plasma membrane, especially through SOCs. Preferred access of SOC‐transported Ca 2+ to VRAC suggests colocalization of these channels in the cell membrane.