Effect of H+ on force development of the heart muscle under acute respiratory failure by cyanide

Force decay of slowly paced (12/min) isometric ventricular strips of frog heart at low temperature (+12 degrees C) was studied under standard cellular respiratory failure (3 mM NaCN). An exponential force decay obtained at pH0 6.0 was transformed to two-step decline by increasing the pH0. The rapid phase of the force decline was pH insensitive. The slope of the second slow phase was regulated by pH0 between 6.0 and 7.7 (force reduction to 50 percent was 7 min at pH 6.0 and more than 60 min at 7.7). This effect was partially blocked by citrate (1.5-3.0 mM). Data obtained are compared with pH values measured within the normal and ischemic myocardium and are discussed with respect to the role of proton accumulation and diffusion within the ischemic ventricular wall.