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Protective effects of lactic acid on force production in rat skeletal muscle

By Ole B Nielsen, Frank de Paoli and Kristian Overgaard

Abstract

During strenuous exercise lactic acid accumulates producing a reduction in muscle pH. In addition, exercise causes a loss of muscle K+ leading to an increased concentration of extracellular K+ ([K+]o). Individually, reduced pH and increased [K+]o have both been suggested to contribute to muscle fatigue.To study the combined effect of these changes on muscle function, isolated rat soleus muscles were incubated at a [K+]o of 11 mm, which reduced tetanic force by 75 %. Subsequent addition of 20 mm lactic acid led, however, to an almost complete force recovery. A similar recovery was observed if pH was reduced by adding propionic acid or increasing the CO2 tension.The recovery of force was associated with a recovery of muscle excitability as assessed from compound action potentials. In contrast, acidification had no effect on the membrane potential or the Ca2+ handling of the muscles.It is concluded that acidification counteracts the depressing effects of elevated [K+]o on muscle excitability and force. Since intense exercise is associated with increased [K+]o, this indicates that, in contrast to the often suggested role for acidosis as a cause of muscle fatigue, acidosis may protect against fatigue. Moreover, it suggests that elevated [K+]o is of less importance for fatigue than indicated by previous studies on isolated muscles

Topics: Rapid Report
Publisher: Blackwell Science Inc
OAI identifier: oai:pubmedcentral.nih.gov:2278832
Provided by: PubMed Central
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