PROPERTIES OF A CELL VOLUME-SENSITIVE POTASSIUM CONDUCTANCE IN ISOLATED GUINEA-PIG AND RAT HEPATOCYTES

1. Whole-cell voltage clamp and intracellular recording techniques were used to study the increase in K+ conductance that accompanies swelling in isolated guinea-pig and rat hepatocytes in short-term culture at 37-degrees-C. 2. Swelling was induced (i) by the application of pressure (15 cmH2O) to the shank of the patch pipette, (ii) by exposing the cells to hypotonic solutions and (iii) as a consequence of leakage of electrolyte from an intracellular microelectrode. 3. Applying pressure to the patch pipette caused a large outward current (approximately 600 pA) to develop in guinea-pig hepatocytes voltage clamped to 0 mV. This current reversed direction at -86 mV, close to the reversal potential for K+, E(K) (-93 mV), and is attributable to the activation of a K+ conductance. 4. Spectral analysis of current noise during this response suggested a single-channel conductance of 7 pS, though this may well be an underestimate. The power spectrum could be fitted by the sum of two Lorentzian components, with half-power frequencies of 7 and 152 Hz. Seventy per cent of the variance was associated with the lower frequency component. 5. The steady-state current-voltage relationship for guinea-pig hepatocytes, as determined by whole-cell recording, was linear over the range -70 to +40 mV both before and during the increase in K+ conductance induced by swelling. 6. Confirming earlier work, intracellular recording using microelectrodes filled with 1 M-potassium citrate sometimes resulted in a slow hyperpolarization and a large rise in input conductance. These changes are also attributable to an increase in K+ conductance as the cell swelled because of leakage from the electrode. 7. Application of hypotonic external solutions during intracellular recording caused hyperpolarization and an increase in conductance. Conversely, hypertonic solution evoked depolarization and a fall in conductance in partly swollen cells. 8. The volume-activated K+ conductance was reversibly blocked by cetiedil, which caused half-maximal inhibition at 2.3-mu-M. Bepridil, quinine and barium were also effective, with IC50S (concentrations giving 50% maximal inhibition) of 2.7, 12 and 67-mu-M respectively. 9. Much greater concentrations of cetiedil and bepridil (IC50 approximately 1 mM and 77-mu-M respectively) were required to inhibit the loss of K+ which follows the application of angiotensin II (100 nM) to guinea-pig hepatocytes, and which occurs via Ca2+- activated K+ channels. Our evidence suggests that the activation of K+ channels by cell swelling is Ca2+ independent. 10. Oligomycin A (2 and 15-mu-M) and oxpentifylline (20 and 100-mu-M) were ineffective, indicating that the cetiedil-sensitive K+ channels in hepatocytes differ from those in lymphocytes and red blood cells. 11. In summary, swelling causes the opening of low conductance K+ channels in hepatocytes. The channels are potently blocked by cetiedil and bepridil, and their opening is not mediated by internal Ca2+.