Calcium currents of ventricular cell pairs during action potential
conduction.
Kumar, Rajiv, and Ronald W. Joyner.
Todd Franklin Cardiac Research Laboratory, The Children's Heart Center,
Department of Pediatrics, Emory University, Atlanta, GA, 30323
APStracts 2:0009H, 1995.
We have studied the L-type calcium current that occurs during action potential
conduction between an isolated pair of guinea pig ventricular cells. To
accomplish this, we first recorded action potentials from the leader cell
(stimulated cell, cell 1) and the follower cell (non-stimulated cell, cell 2)
with a fixed coupling resistance between the cells supplied by a coupling
clamp circuit. We then applied these recorded action potentials as command
potential waveforms for other cells studied in the voltage clamp mode in
which internal and external solutions which isolated the L-type calcium
current were used. The action potential waveform of the leader cell had a
rapid upstroke and then a partial repolarization during the conduction delay
before activation of the follower cell. The L-type calcium current occurred
with a large magnitude during the conduction delay for the leader cell but
not for the follower cell. This leads to an asymmetry of calcium current for
the two cells, with greater calcium current for the leader cell than for the
follower cell. When we reversed the direction of conduction for cell 1 and
cell 2 by stimulating cell 2, we found that application of these recorded
waveforms for the action potentials for cell 1 and cell 2 to the voltage
clamped cells also reversed the asymmetry of the magnitude of the calcium
current. We conclude that discontinuous conduction in cardiac tissue is
associated with a directionally determined asymmetry in the magnitude of the
calcium current, with the leader cell experiencing a greater peak calcium
current than the follower cell.
Received 14 July 1994; accepted in final form 10 January 1995.
APS Manuscript Number H615-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 24 February 1995.