FUNCTIONAL-SIGNIFICANCE OF K- CHANNELS IN VOLUME REGULATION IN PROXIMAL TUBULAR CELLS( AND CL)

Using the patch-clamp technique to cultured opossum kidney (OK) cells, we measured the activities of K+ channel and Cl- conductance during h yposmotic stress. The results are as follows: 1) A 50% lowered osmolar ity of bath media induced a biphasic change of the membrane potential (E(M)): early hyperpolarization and late depolarization. The former tr ansient response was abolished by removing Ca2+ from the cellular medi a, whereas the latter slow response was blocked by DIDS. 2) The hyposm osis-induced change of E(M) was due to K+ channels activated by cytoso lic Ca2+. 3) In hyposmotic media, Cl- current was effectively increase d, and this effect was abolished by Cl- channel blockers. 4) The hypos mosis-induced Cl- conductance was inhibited in; the cytosolic acid med ia. In the alkaline media, it was enhanced even without hyposmotic str ess. We conclude that the hyposmosis-induced activation of Cl- conduct ance, being stimulated by alkaline cell pH and inhibited by acid cell pH, may contribute to the ion transport and cell volume regulation alo ng with the Ca2+-activated K+ channel.