A Role of Subcellular Factors to Control Channels in Kidney Tubules.

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Using the patch-clamp technique, we investigated a mechanism of activation of single-channel currents during cell volume regulation in cultured rabbit kidney proximal tubule cells. Hypotonically induced cell-swelling increased Ca-dependent K currents, and then, Cl currents. Because cell membrane potential initially hyperpolarized, and then returned to the original level with KCl in the pipette (current-clamp mode). Omitting extracellular Ca from and adding 0.1 mM EGTA to the bath solution significantly slowed a time course of cell volume regulation. At Vp=0 mV the whole-cell K currents induced by hypotonicity decreased by 90% when a pipette-filling solution contained zero Ca and 5 mM EGTA. Addition of 5 mM Ba to the bath almost completely inhibited K currents due to cell-swelling. Activation of Cl currents due to hypotonicity was partially inhibited by either 20 uM SITS in the bath or zero Ca plus 5 mMEGTA in the pipette(whole-cell clamp condition).In conclusion, hypotonicallyinduced cell swelling stimulates Ca-activated K channels, which may play an important role in cell volume regulation. A secondary activation of Cl currents may also be essential for the regulatory volume decrease mechanism.