Effects of Acidosis on Maximum Shortening Velocity and Force-Velocity Relation of Skinned Rat Cardiac Muscle

Abstract

This study was designed to assess whether maximum shortening velocity and force-velocity parameters were reduced by acidosis in rat skinned cardiac trabeculae, as reported for skinned skeletal muscles. Thin trabeculae were dissected from right ventricle of adult male Wistar rats, chemically skinned, and maximally Ca-activated at pH 7.0, 6.6 and 6.2. Maximum tension (P o), maximum shortening velocity evaluated from force-velocity curves (V max), and maximum power output (W max) were significantly reduced for exposure to pH 6.6 and 6.2. When the value at pH 7.0 is taken as reference, P o decreased by 30% and 49% V max by 17% and 40% and W max by 30% and 60% at pH 6.6 and 6.2 respectively. A similar reduction (25% at pH 6.6 and 42% and pH 6.2) was observed when unloaded shortening velocity (V o) was determined with the slack test method. The results obtained show that both P o and V max or V o, are affected by a substantial decrease in pH. The combination between significantly lower P o and V max gives rise to significantly lower W max. The reduction of maximum shortening velocity (V max or V o) can be explained by assuming either the existence of an internal load or an impairment in actin-myosin interaction.