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1 Department of Biomedical
Engineering, Tulane University, New Orleans, Louisiana 70125;
2 Department of Medicine,
Conduction at the Purkinje-ventricular
junction (PVJ) demonstrates unidirectional block under both
physiological and pathophysiological conditions. Although this block is
typically attributed to multidimensional electrotonic interactions, we
examined possible membrane-level contributions using single, isolated
rabbit Purkinje (P) and ventricular (V) myocytes coupled by an
electronic circuit. When we varied the junctional resistance
(Rj) between
paired V myocytes, conduction block occurred at lower
Rj values during
conduction from the smaller to larger myocyte (115 ± 59 M
) than
from the larger to smaller myocyte (201 ± 51 M
). In
Purkinje-ventricular myocyte pairs, however, block occurred at lower
Rj values during
P-to-V conduction (85 ± 39 M
) than during V-to-P conduction (912 ± 175 M
), although there was little difference in the mean cell
size. Companion computer simulations, performed to examine how the
early plateau currents affected conduction, showed that P-to-V block
occurred at lower Rj values when
the transient outward current was increased or the calcium current was
decreased in the model P cell. These results suggest that intrinsic
differences in phase 1 repolarization
can contribute to unidirectional block at the PVJ.
action potential propagation; coupling-clamp circuit; membrane models; transient outward current; discontinuous conduction
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