Role of the nervous system in regulation of the sarcoplasmic membrane function in different muscle fibres.

The influence of the nervous system on the Ca2+ uptake of sarcoplasmic reticulum (SR) of the slow-twitch and fast-twitch muscle was investigated by the application of denervation, immobilization and tenotomy. Denervation and immobilization produced an increase of Ca2+ uptake in SR of the slow-twitch muscle. No significant change could be observed in fast-twitch muscle. Inactivity atrophy induced by tenotomy had no effect on the Ca2+ uptake in SR of the slow muscle. The results suggest that the nervous system has a greater effect on SR function in the slow than in the fast-twitch muscle. The continuous effect of the nervous system characteristic of slow-twitch muscle fibres with tonic function plays a role in preservation of the low Ca2+ uptake capacity, in contrast to the fast-twitch muscle fibres with phasic function, which have a high Ca2+ uptake capacity.