AJP - Heart and Circulatory Physiology, Vol 253, Issue 2 373-H379, Copyright © 1987 by American Physiological Society
Action potential duration in ventricular muscle during selective metabolic block
H. Hayashi, T. Watanabe and T. F. McDonald
We have examined whether maintenance of the cardiac action potential
duration depends exclusively on energy from glycolysis. Oxidative
phosphorylation in guinea pig papillary muscles was inhibited by
superfusion with hypoxic solutions. After 60 min in 50 mM glucose solution,
the action potential duration was 85% of aerobic control, but ATP content
was only 25%; after 60 min in 0 mM glucose, both the duration and ATP
content had declined to 15% control. When the glucose concentration of
hypoxic solution was raised from 0 to 50 mM, there was nearly full recovery
of the action potential duration but ATP only increased to about 25%
control. We attribute action potential shortening during metabolic
inhibition to suppression of calcium current and activation of potassium
current; the latter are graded in intensity and expressed only at low ATP.
When normoxic muscle was treated with 20 mM 2-deoxy-D-glucose (2-DG) to
inhibit glycolysis, there was an early transient shortening of the action
potential. This was attributed to ATP consumption related to early rapid
2-DG influx and phosphorylation. After the transient, the action potential
duration was maintained for several hours in oxygenated 2-DG solution. The
duration was also maintained in oxygenated muscle depleted of glycolytic
substrate. Thus we found no evidence of an exclusive relation between
action potential duration and glycolysis.
