AJP - Heart and Circulatory Physiology, Vol 244, Issue 3 341-H350, Copyright © 1983 by American Physiological Society
Outward current and repolarization in hypoxic rat myocardium
C. H. Conrad, R. G. Mark and O. H. Bing
We studied the effects of brief periods (20-30 min) of hypoxia in the
presence of 5 and 50 mM glucose and of glycolytic blockade (10(-4) M
iodoacetic acid, IAA) on action potentials, membrane currents, and
mechanical activity in rat ventricular papillary muscles using a single
sucrose gap voltage-clamp technique. Steady-state outward current (iss) was
determined at the end of a 500-ms clamp to the test potential following a
600-ms clamp to a holding potential of -50 mV. In the presence of 5 mM
glucose, hypoxia resulted in a decrease in action potential duration (APD)
and an increase in iss (on the order of 60% at 0 mV) over the potential
range studied. The increase in iss did not appear to be due to an increase
in leakage current or to a change in the cable properties of the
preparation. Addition of 50 mM glucose prevented the change in both APD and
iss with hypoxia. In addition, glycolytic blockade with IAA did not alter
iss in the presence of oxygen. We conclude that an increase in iss appears
to be a major factor in the abbreviation of rat ventricular action
potential seen with hypoxia. Glycolysis appears to be a sufficient (with 50
mM glucose) but not necessary source of energy for the maintenance of
normal iss.
