Ca2+ modulation of volume-regulated anion channels:: evidence for colocalization with store-operated channels

Ca2+ regulation of Cl- current induced by cell swelling (I-Cl,I-swell) in response to hypotonicity was studied in human prostate cancer epithelial cells (LNCaP) by using the patch-clamp technique. Increase of global intracellular Ca2+ ([Ca2+](in)) to 1 muM as well as variations of the extracellular Ca2+ ([Ca2+](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,I-swell. However, the presence of 0.1 muM thapsigargin (TG), an inhibitor of endoplasmic reticulum (ER) Ca2+ pump, resulted in a more than 50% inhibition of I-Cl,I-swell. The blockade of plasma membrane store-operated channels (SOCs), activated in the presence of TG, by 2 mM Ni2+ prevented TG-conferred I-Cl,I-swell inhibition by extracellular Ca2+. In the presence of TG and Ca2+, the cells failed to exhibit regulatory volume decrease. We conclude that interaction between volume-regulated anion channels (VRACs) carrying I-Cl,I-swell and Ca2+ occurs in the microdomains from the inner surface of the membrane that are not accessible to the changes in [Ca2+](in), but can be readily reached by Ca2+ entering the cell via plasma membrane, especially through SOCs. Preferred access of SOC-transported Ca2+ to VRAC suggests colocalization of these channels in the cell membrane.