The effects of nitric oxide on the maximum shortening velocity of frog and mouse skeletal muscle

Francaux, M. [UCL] Beckers-Bleukx, G. Maréchal, Georges [UCL]

The maximal velocity of shortening ( Vmax) is the single most important mechanical parameter of skeletal muscle fibres, since it indicates the maximum rate of cross-bridge cycling in the muscle. It is measured from the time needed to take up a slack after a rapid release (Edman, 1979). Vmax varies considerably among muscles, because of differences between myosin isoforms. Muscle fibres, are able to change their phenotype by suppressing the expression of a myosin isoform and expressing another one, as for example by training. This process is slow, however, requiring several weeks, because the turnover of myosin is quite slow. Up to now, no physiological factor has been reported that might modulate Vmax of a living skeletal muscle within a time scale of a few seconds. We report here on a mechanism to control Vmax that, in contrast to the genetic mechanism, acts very quickly, possibly within a time scale of a few seconds. It is based on the local production of nitric oxide (NO), a radical whose half-life is very short in tissues.