Hypotonically induced whole-cell currents in A6 cells: relationship with cell volume and cytoplasmic Ca2+.
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.
Yu
W G
WG
Department of Physiology, Nagoya University School of Medicine, Showa-ku Nagoya, 466 Japan.
Sokabe
M
M
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002460:Cell Line; D048429:Cell Size / Q000187:drug effects*; D018118:Chloride Channels / Q000037:antagonists & inhibitors; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism*; D007038:Hypotonic Solutions / Q000494:pharmacology*; D009994:Osmolar Concentration; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers; D014982:Xenopus laevis
D002121:Calcium Channel Blockers; D018118:Chloride Channels; D007038:Hypotonic Solutions; D026902:Potassium Channel Blockers; D002118:Calcium