Effects of hypoxia with mild acidosis and reoxygenation on slow response action potentials in canine myocardial tissues

Abstract

We studied slow response action potentials (SRAP) in canine ventricular muscle tissue during hypoxia (and mild acidosis) and reoxygenation. Slow responses were initiated by perfusing the tissue with a solution containing 27 mM KCl and 10(-6) M norepinephrine. The tissue was stimulated at 0.5 Hz, 20V and 4ms (duration of the pulse). Microelectrode techniques were used to record action potential and mechanical activity was recorded with a force displacement transducer. Hypoxia and mild acidosis progressively diminished the amplitude and duration of these SRAPs, whereas reperfusion/reoxygenation progressively increased their amplitude even more than that in the control (prehypoxic value). Action potential duration (APD) increased (at all levels) during reperfusion compared to that in hypoxia and mild acidosis but APD remained shorter than the control (prehypoxic level). The effects of hypoxia (and mild acidosis) and subsequent reoxygenation seem similar to that of elevating the extracellular calcium (increased inward current). From these experiments one cannot, however, distinguish the effects of hypoxia on inward current from those on the outward currents.