Effects of pH on the length-dependent twitch potentiation in skeletal muscle

Dilson E. Rassier, Walter Herzog
2002 Journal of applied physiology  
Rassier, Dilson E., and Walter Herzog. Effects of pH on the length-dependent twitch potentiation in skeletal muscle. When muscle is elongated, there is a length dependence of twitch potentiation and an increased Ca 2ϩ sensitivity of the myofilaments. Changes in the charge potential of myofilaments, induced by a decrease in pH, are known to abolish the length dependence of Ca 2ϩ sensitivity. This study was aimed at testing the hypothesis that a decrease in pH, and the concomitant loss of length
more » ... ant loss of length dependence of Ca 2ϩ sensitivity, depresses the length dependence of staircase potentiation. In vitro, isometric twitch contractions of fiber bundles dissected from the mouse extensor digitorum longus, performed before and after 10 s of 10-Hz stimulation (i.e., the staircase potentiation protocol) were analyzed at five different lengths, ranging from optimal length for maximal force production (L o; ϭ 12 Ϯ 0.7 mm) to Lo ϩ 1.2 mm (Lo ϩ 10%). These measurements were made at an extracellular pH of 6.6, 7.4, and 7.8 (pH changes induced by altering the CO 2 concentration of the bath solution). At pH 7.4 and 7.8, the degree of potentiation after 10-Hz stimulation showed a linear decrease with increased fiber bundle length (r 2 ϭ 0.95 and r 2 ϭ 0.99, respectively). At pH 6.6, the length dependence of potentiation was abolished, and the slope of the length-potentiation relationship was not different from zero (r 2 ϭ 0.05). The results of this study indicate that length dependence of potentiation in intact skeletal muscle is abolished by lowering the pH. Because decreasing the pH decreases Ca 2ϩ sensitivity and changes the charge potential of the filaments, the mechanism of length-dependent potentiation may be closely related to the length dependence of Ca 2ϩ sensitivity, and changes in the charge potential of the myofilaments may be important in regulating this relationship. force-length relation; Ca 2ϩ sensitivity; force potentiation; twitch force
doi:10.1152/japplphysiol.00912.2001 pmid:11842070 fatcat:l5rbxkqvn5hudfadc4pjwkkoei