Asymmetric voltage-dependence of embryonic cardiac gap junction
channels.
Chen, Yan-Hua, and Robert L. Dehaan.
Department of Anatomy and Cell Biology, Emory University Health
Science Center, Atlanta, GA 30322
APStracts 2:0279C, 1995.
The voltage dependence of junctional conductance (Gj) and the unitary
channel behavior of junctions in most pairs of 3-day, 7-day and 18
-day embryonic chick heart cells are symmetrical, i.e. they are
independent of the direction of polarization of junctional potential
(Vj). With either cell depolarized relative to its neighbor, unitary
channel events have a maximal cj near 240 pS, and five sub-states at
nearly equal 40 pS increments down to near 40 pS (6, 9). Using the
dual patch-clamp technique, we demonstrate here that in a fraction of
such cell pairs, Vj-dependent channel kinetics are asymmetric.
Depolarization of one cell causes a larger and faster voltage
-dependent decline in junctional conductance than the same
depolarization of the other cell. In a typical asymmetric
preparation, depolarization of the strongly Vj-dependent side caused
an immediate series of 47+16 pS closing steps in unitary channel
current (ij), followed by virtual cessation of channel activity.
After depolarization of the less Vj-sensitive side, channel activity
(56+13 pS) continues for many seconds. The large conductance states
(160-240 pS) observed in the electrically symmetric junctions were
absent from the asymmetric preparations. In these cell pairs, Cx42,
Cx43, and Cx45 could be immunolocalized at the junctional surfaces.
We postulate that the asymmetry of voltage dependence in some cell
pairs results from a preponderance of heterochannels formed from
these different connexins. The frequency of asymmetric pairs obtained
from 3-day, 7-day and 18-day embryonic hearts was 50% (4/8), 24%
(6/25) and 12.5% (1/8), suggesting that the fraction of
heterochannels in the junctions decreases with cardiac development.
Received 6 June 1994; accepted in final form 14 July 1995.
APS Manuscript Number C302-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 July 1995.