The influence of physiological l(+)-lactate concentrations on contractility of skinned striated muscle fibers of rabbit. Andrews, Mark Anthony W., Robert E. Godt, and Thomas M. Nosek. Division of Physiology, New York College of Osteopathic Medicine, Old Westbury, NY 11568; Department of Physiology and Endocrinology, Medical College of Georgia, Augusta, GA 30912-3000
APStracts 3:0076A, 1996.
These experiments investigated the effects of physiological concentrations of L(+)-lactate on the contractility of chemically -skinned rabbit fast-twitch psoas, slow-twitch soleus, and cardiac muscle at pH 7. L(+)-lactate depressed maximal calcium-activated force (Fmax) of all muscles studied, within the range of 5-20 (slow -twitch) or 5-25 mM (fast-twitch and cardiac muscle). Fmax of fast -twitch fibers was inhibited to the greatest degree (9% in K2creatine phosphate solutions). In all of these muscle types Fmax returned to control levels as L(+)-lactate was increased to 30 - 50 mM. Substitution of neither D-lactate nor propionate for L(+)-lactate significantly altered Fmax. In addition, with the exception of fast -twitch muscle (where the Hill coefficient decreased), L(+)-lactate concentrations which maximally inhibited Fmax did not affect the force vs. pCa relationship of muscles tested. These results demonstrate that L(+)-lactate significantly contributes to the depression of muscle function noted during lactic acidosis, directly inhibiting Fmax of the contractile apparatus. This contribution is maximal in fast-twitch muscle where L(+)-lactate is responsible for as much as one-third of the depressant effect on Fmax of the contractile apparatus noted during lactic acidosis. 

Received 29 July 1994; accepted in final form 22 January 1996.
APS Manuscript Number A779-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 8 February 96