Effects of denervation and immobilisation during development upon [3H]ouabain binding by slow- and fast-twitch muscle of the rat.

The effect of innervation and of muscle inactivity upon the normal production of Na+-K+-ATPase sites, assayed by [3H]ouabain binding, in muscle surface membranes has been determined for the rat. In both slow-twitch soleus (SOL) and fast-twitch extensor digitorum longus (EDL) muscles a large increase was found to occur in [3H]ouabain binding per unit weight of muscle over the first 3 weeks of life. Interruptions of development, brought about by fixation of muscles at different lengths at 5 days of age, had no significant effect upon [3H]ouabain binding by EDL. In contrast, fixation led to a decrease in binding in SOL. When fixed in a shortened position profound morphological changes occurred, although these were not apparent when SOL was fixed in a stretched position. Denervation of SOL at 5 days of age significantly reduced the age related increase in the density of [3H]ouabain binding, whilst denervation of EDL had little effect. It was concluded that normal development of SOL is dependent upon innervation and possibly the resulting muscle activity, whereas development of EDL was relatively independent of innervation.