Functional significance of K+ and Cl- channels in volume regulation in proximal tubular cells.
Using the patch-clamp technique to cultured opossum kidney (OK) cells, we measured the activities of K+ channel and Cl- conductance during hyposmotic stress. The results are as follows: 1) A 50% lowered osmolarity of bath media induced a biphasic change of the membrane potential (EM): early hyperpolarization and late depolarization. The former transient response was abolished by removing Ca2+ from the cellular media, whereas the latter slow response was blocked by DIDS. 2) The hyposmosis-induced change of EM was due to K+ channels activated by cytosolic Ca2+. 3) In hyposmotic media, Cl- current was effectively increased, and this effect was abolished by Cl- channel blockers. 4) The hyposmosis-induced Cl- conductance was inhibited in the cytosolic acid media. In the alkaline media, it was enhanced even without hyposmotic stress. We conclude that the hyposmosis-induced activation of Cl- conductance, being stimulated by alkaline cell pH and inhibited by acid cell pH, may contribute to the ion transport and cell volume regulation along with the Ca(2+)-activated K+ channel.
Fujimoto
M
M
Department of Physiology, Osaka Medical College, Japan.
Mori
Y
Y
Hagiwara
N
N
Kubota
T
T
Kotera
K
K
D000818:Animals; D018118:Chloride Channels / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport; D007668:Kidney / Q000502:physiology*; D009893:Opossums; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000502:physiology*; D014882:Water-Electrolyte Balance
D018118:Chloride Channels; D015221:Potassium Channels