AJP - Cell Physiology, Vol 262, Issue 6 C1531-C1538, Copyright © 1992 by American Physiological Society
Mechanism of heptanol-induced uncoupling of cardiac gap junctions: a perforated patch-clamp study
B. R. Takens-Kwak, H. J. Jongsma, M. B. Rook and A. C. Van Ginneken
Department of Physiology, University of Amsterdam, The Netherlands.
The influence of heptanol on gap junctional and non-junctional membrane
currents was studied in cultured neonatal rat heart cells using both the
whole cell and perforated patch voltage-clamp method. With both methods,
exposure to heptanol produced a dose-dependent decrease in the junctional
current (dissociation constant = 0.54 and 1.20 mM for whole cell and
perforated patch experiments, respectively). Heptanol-induced uncoupling
was reversible. In the same concentration range, heptanol reduced all
nonjunctional membrane ionic currents examined. This suggests that heptanol
does not act specifically on gap junction channels but rather on the
structure of the lipid membrane. This hypothesis is strengthened by the
observation that in monolayer cultures of neonatal rat heart cells
fluorescence steady-state anisotropy decreased proportional with increasing
the heptanol concentration in the bath. Single-channel conductances (gamma
j) were identical with both recording methods (21 and 40-45 pS); heptanol
did not alter gamma j. Under conditions of reduced junctional coupling
induced by heptanol, junctional conductance (gj) displayed voltage
sensitivity at values of gj at which no voltage sensitivity could be
observed under control conditions. These results suggest that
heptanol-dependent uncoupling was caused by a decrease in open probability
of the gap junction channels.
