Early effects of denervation on sarcoplasmic reticulum properties of slow-twitch rat muscle fibres.
The Ca2+ release activity of the sarcoplasmic reticulum (SR) in chemically skinned single slow-twitch fibres from control, 2-day and 7-day denervated rat soleus muscle was studied. Histochemical fibre type composition of the whole muscle, electrophysiological properties and the Ca2+ sensitivity of tension development by single muscle fibres were also studied. All the data were correlated with contractile properties of the in vitro muscle. In the 2-day denervated muscle the SR Ca2+ capacity and the rate of Ca2+ uptake decreased from the control values of 0.384 +/- 0.030 micromol (mg fibre protein)-1 and 19.8 +/- 1.9 nmol min-1 (mg fibre protein)-1, respectively, to 0.210 +/- 0.016 micromol (mg fibre protein)-1 and 13.5 +/- 0.9 nmol min-1 (mg fibre protein)-1; the calculated amount of Ca2+ released upon stimulation by caffeine decreased from the control value of 0.148 to 0.078 micromol (mg fibre protein)-1. In the 7-day denervated muscle, the SR Ca2+ capacity and the rate of Ca2+ uptake increased to 0.517 +/- 0.06 micromol (mg fibre protein)-1 and 21.6 +/- 2.3 nmol min-1 (mg fibre protein)-1, respectively; the calculated amount of Ca2+ released increased to 0.217 micromol (mg fibre protein)-1. Both contraction time and tension of the isometric twitch decreased in 2-day denervated and increased in 7-day denervated muscles. Electrophysiological and histochemical changes, as well as changes in the Ca2+ sensitivity of the muscle fibres did not show any apparent correlation with mechanical changes. It is therefore concluded that the SR plays a prominent role in the early changes of contraction time and tension following denervation.
Midrio
M
M
Institute of Human Physiology, University of Padova, Via Marzolo 3, I-35131 Padova, Italy.
Danieli-Betto
D
D
Megighian
A
A
Betto
R
R
D000818:Animals; D002118:Calcium / Q000378:metabolism; D004594:Electrophysiology; D005528:Foot; D006651:Histocytochemistry; D009119:Muscle Contraction / Q000502:physiology; D009121:Muscle Denervation; D018657:Muscle Fibers, Slow-Twitch / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation; D051381:Rats; D017208:Rats, Wistar; D012519:Sarcoplasmic Reticulum / Q000378:metabolism / Q000502:physiology*
D002118:Calcium