Key result
In rabbit glycerinated skeletal muscle, 50 mM lactate did not significantly affect isometric tension, shortening velocity, or stiffness, whereas decreased pH markedly impaired contractile performance.
Lactate anions do not directly impair skeletal muscle contractile performance, but the associated decrease in pH does.
pH, not lactate, impairs skeletal muscle contractility in this model; leaves open translation to human cardiac or exercise physiology.
To know whether L(+)-lactate directly induces the decrease in muscle contractile performance, several parameters of cross-bridge function were measured at various concentrations of lactate and pH in glycerinated rabbit psoas and soleus muscles at three different temperatures (5, 20, 28 degrees C). At all pHs studied (pH 7.0, 6.5, 6.0, and 5.5), isometric tension, unloaded velocity of shortening, and stiffness of a fiber during active and resting state in the presence of 50 mM lactate were not virtually different from those in the absence of lactate, but pH had remarkable effects on these parameters. The active stiffness decreased only slightly, and the small resting stiffness appeared at low pH; they were not affected by the presence of lactate. The present results indicate that the lactate anions may not have marked influence on the interaction between actin and myosin, and the concomitant change in pH with the production of lactate may remarkably affect it, as far as they were examined under the existing conditions of the experimental solutions.
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Miyake et al. (2003) studied Healthy (animal model). L(+)-lactate vs. Absence of lactate was evaluated on Isometric tension (p=>0.05). In rabbit glycerinated skeletal muscle, 50 mM lactate did not significantly affect isometric tension, shortening velocity, or stiffness, whereas decreased pH markedly impaired contractile performance.
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