The Journal of General Physiology, Vol 91, 255-274, Copyright © 1988 by The Rockefeller University Press
A whole-cell and single-channel study of the voltage-dependent outward potassium current in avian hepatocytes
C Marchetti, RT Premont and AM Brown
Department of Physiology and Molecular Biophysics, Baylor College of Medicine, Houston, Texas 77030.
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.
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