Hypotonically induced whole-cell currents in A6 cells: relationship with cell volume and cytoplasmic Ca2+ |
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Authors: | WG Yu M Sokabe |
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Affiliation: | Department of Physiology, Nagoya University School of Medicine, Showa-ku Nagoya, 466 Japan. |
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Abstract: | We investigated changes in whole-cell currents, cell volume, and intracellular calcium concentration (Ca2+]i) during hypotonic stimulation in whole-cell clamped cultured amphibian renal cells (A6 cells). Upon being exposed to hypotonic solution (80% osmolality), the A6 cells swelled and peaked in the first 5 min, which was followed by a progressive decrease in cell volume termed regulatory volume decrease (RVD). Following the cell swelling, there were large increases in both outward- and inward-currents, which seemed to be carried by K+ efflux and Cl- efflux, respectively. A K+ channel blocker (TEA or quinine) or a Cl- channel blocker (NPPB or SITS) significantly inhibited both currents and RVD, suggesting that the inward- and outward-currents are highly correlated with each other and essential to RVD. Hypotonic stimulation also induced a transient Ca2+]i increase, of which the time course was essentially similar to that of the currents. When internal and external Ca2+ were deprived to eliminate the Ca2+ transient increase, whole-cell currents and RVD were strongly inhibited. On the other hand, channel blockers TEA and NPPB, which inhibited whole-cell currents and RVD, did not inhibit the Ca2+]i increase. It is concluded that hypotonic stimulation to A6 cells first induces cell swelling, which is followed by Ca2+]i increase that leads to the coactivation of K+ and Cl- channels. This coactivation may accelerate K+ and Cl- effluxes, resulting in RVD. |
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