Discontinuous conduction at the purkinje-ventricular muscle
junction.
Wiedmann, Richard T., Rosemarie C. Tan, and Ronald W. Joyner.
The Todd Franklin Cardiac Research Laboratory, The Children's Heart
Center, Department of Pediatrics, Emory University School of
Medicine, 2040 Ridgewood Dr. NE, Atlanta GA, 30322
APStracts 3:0125H, 1996.
Conduction through the cardiac syncytium varies from being nearly
continuous, with very well-coupled cells, to being clearly
discontinuous with significant conduction delays over very short
distances. The Purkinje-Ventricular Muscle Junction (PVJ) sites on
the endocardial surface have characteristic delays of conduction and
the presence of discrete groups of cells which suggest significant
discontinuities of the conduction process at PVJ sites, as compared
to the more nearly continuous conduction within either the Purkinje
or the Ventricular Muscle layers of the Papillary muscle.. The
purpose of the present study was to examine the relative sensitivity
of conduction at PVJ sites, versus conduction within the Purkinje or
the ventricular muscle layer, of the canine papillary muscle to
agents which modulate L-type Calcium current. We have used Cadmium as
a relatively specific blocker of L-type calcium current and
Isoproterenol as an agent to increase L-type Calcium current in order
to test the hypothesis that discontinuous conduction, at the PVJ
sites, would be more sensitive to these agents than would the
continuous conduction within either the Purkinje layer or the
ventricular muscle layer of a canine papillary muscle. Conduction
delay at the PVJ sites was significantly increased by Cadmium, with
some PVJ sites reversibly becoming non-junctional at 200-400 [mu]M
Cadmium. Isoproterenol significantly decreased PVJ delay and this
effect was attenuated by Carbachol. All of the effects on conduction
delay at the PVJ sites were much greater than the effects for the
same agents on conduction velocity within either the Purkinje or the
Ventricular Muscle layer of the papillary muscle.
Received 28 November 1995; accepted in final form 29 February
1996.
APS Manuscript Number H1109-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 1 April 96