A whole-cell and single-channel study of the voltage-dependent outward potassium current in avian hepatocytes.
Voltage-dependent membrane currents were studied in dissociated hepatocytes from chick, using the patch-clamp technique. All cells had voltage-dependent outward K+ currents; in 10% of the cells, a fast, transient, tetrodotoxin-sensitive Na+ current was identified. None of the cells had voltage-dependent inward Ca2+ currents. The K+ current activated at a membrane potential of about -10 mV, had a sigmoidal time course, and did not inactivate in 500 ms. The maximum outward conductance was 6.6 +/- 2.4 nS in 18 cells. The reversal potential, estimated from tail current measurements, shifted by 50 mV per 10-fold increase in the external K+ concentration. The current traces were fitted by n2 kinetics with voltage-dependent time constants. Omitting Ca2+ from the external bath or buffering the internal Ca2+ with EGTA did not alter the outward current, which shows that Ca2+-activated K+ currents were not present. 1-5 mM 4-aminopyridine, 0.5-2 mM BaCl2, and 0.1-1 mM CdCl2 reversibly inhibited the current. The block caused by Ba was voltage dependent. Single-channel currents were recorded in cell-attached and outside-out patches. The mean unitary conductance was 7 pS, and the channels displayed bursting kinetics. Thus, avian hepatocytes have a single type of K+ channel belonging to the delayed rectifier class of K+ channels.
D015761:4-Aminopyridine; D000631:Aminopyridines / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000502:physiology; D002478:Cells, Cultured; D002645:Chickens; D004553:Electric Conductivity; D004594:Electrophysiology; D007473:Ion Channels / Q000502:physiology*; D007700:Kinetics; D008099:Liver / Q000166:cytology / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials; D011188:Potassium / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology
D000631:Aminopyridines; D007473:Ion Channels; D013779:Tetrodotoxin; D015761:4-Aminopyridine; D011188:Potassium; D002118:Calcium