AJP - Heart and Circulatory Physiology, Vol 258, Issue 6 1906-H1917, Copyright © 1990 by American Physiological Society
Time delays in propagation of cardiac action potential
D. A. Israel, D. J. Edell and R. G. Mark
Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge 02139.
Recent work has suggested that discrete time delays could occur between
cardiac cells under physiological conditions. To investigate the existence
of such time delays, monolayers of 10-day chick-embryo ventricular myocytes
were grown in cell culture on arrays of extracellular microelectrodes. The
most closely spaced recording electrodes were on 20-microns centers. Some
pairs of electrodes recorded from different points on the same cell,
whereas other pairs straddled intercellular junctions. The preparation was
electrically paced to obtain a repeatable propagation pathway. Arrival
times of activation at each microelectrode were measured. After control
recordings, the preparation was exposed to medium containing 20 mM NH4Cl
for 15 min and then returned to normal medium. This intervention produces
transient intracellular acidification that decreases intercellular
coupling. After acidification, the average (multicellular) conduction
velocity decreased to about two-thirds of the control value. Propagation
velocity measured between most electrode pairs decreased proportionately.
However, disproportionately long propagation delays of up to 410
microseconds were observed between some pairs of electrodes in various
experiments. The delays recovered as pH returned to normal. The localized
long delays were thought to be due to decreased intercellular coupling at
gap junctions.
