Involvement of Intracellular Ca²⁺ in the Regulatory Volume Decrease After Hyposmotic Swelling in MDCK Cells

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We examined the source of Ca²⁺ involved in the volume regulation of Madin-Darby canine kidney (MDCK) cells with confocal microscopy and fluoroprobes. Hyposmosis induced a transient increase in cell volume, as well as cytoplasmic Ca²⁺, which peaked at 3 to 5 min and gradually decreased to reach the initial value within about 30 min. This late decrease in cell volume, as well as the transient rise in cytoplasmic Ca²⁺, was reduced in Ca²⁺-free solution and was abolished by pretreatment with thapsigargin. In conclusion, Ca²⁺ released from the intracellular store contributes to the regulatory volume decrease following hyposmotic swelling in MDCK cells.