NOVEL ACTIVATION STIMULUS OF CHLORIDE CHANNELS BY POTASSIUM IN HUMAN OSTEOBLASTS AND HUMAN LEUKEMIC T-LYMPHOCYTES

1. The whole-cell recording mode of the patch-clamp technique was used to study the effect of extracellular K+ and Rb+ on membrane currents in human osteoblasts, in a human osteoblast-like cell line, and in the Jurkat human leukaemic T cell line. 2. Increasing the extracellular c oncentration of K+ increased the membrane conductance of the cells in a concentration-dependent manner. This increase in membrane conductanc e was due to the activation of a Cl- conductance. Rb+ also induced thi s conductance, but conductance was less than half that seen in K+. 3. The Cl- channel blockers 4,4'-diisothiocyanatostilbene-2,2'-disulphoni c acid (DIDS) and 4-acetamido-4'-isothiocyanatostilbene 2,2'-disulphon ic acid (SITS) blocked the K+-induced Cl- current in a voltage-depende nt manner. The degree of blockade increased with membrane depolarizati on to a maximum level at 40 mV. At potentials above this value the blo ck appeared to decrease. 4. Both tonicity and K+ were required for max imal activation of the Cl- conductance since the K+-induced Cl- conduc tance could be inhibited by hypertonic solutions and the activation of a volume-sensitive Cl- conductance by hypotonic solutions could be en hanced by extracellular K+. 5. We conclude that an outwardly rectifyin g Cl- conductance can be activated either upon osmotic swelling or by an increase in extracellular K+. Both activation pathways may be invol ved in cell volume regulation and seem to apply to volume-sensitive Cl - channels in general since we observe this phenomenon in two differen t cell types, in human osteoblasts as well as in human leukaemic T lym phocytes.