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

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.