AJP - Cell Physiology, Vol 258, Issue 4 C662-C672, Copyright © 1990 by American Physiological Society
Voltage-dependent gating of gap junction channels in embryonic chick ventricular cell pairs
R. D. Veenstra
Department of Pharmacology, State University of New York, Syracuse 13210.
The dependence of macroscopic gap junctional conductance (Gj) on
transjunctional voltage (Vj) was studied in paired myocytes after enzymatic
dissociation of 7-day-old embryonic chick ventricles. The membrane voltage
of both cells was independently controlled by separate patch-clamp circuits
in the whole cell configuration. Two distinctive unitary junctional
conductances were identified in recordings from seven different cell pairs.
The larger channel had a mean conductance of 166 +/- 37 pS (n = 6 pairs),
whereas a second channel averaged 58 +/- 10 pS (n = 3). Instantaneous Gj
remained linear over a Vj range of -100 to +100 mV, whereas the
steady-state Gj declined when voltages exceeded +/- 30 mV. Both decay and
recovery phases of Gj follow exponential time courses, with the recovery
time constant being four times slower than inactivation, requiring 1.1 s at
80 mV. The normalized steady-state Gj-Vj curve could be defined by a
two-state Boltzmann distribution, assuming an effective gating charge of
1.72, a half-inactivation voltage of 45 mV, and a residual
voltage-insensitive Gj of 27% of maximum. Single-channel recordings
revealed closure of 160-pS channels on a Vj step to 80 mV, and the ensemble
average of five such records produced an exponentially decaying junctional
current with a time constant of 184 ms. The single-channel current-voltage
relationship remains linear with a slope of 145 pS over the entire Vj
range. The results support the hypothesis that a population of 160-pS gap
junction channels is gated by transjunctional potentials.
