EFFECTS OF 4 WK OF HINDLIMB SUSPENSION ON SKELETAL-MUSCLE MITOCHONDRIAL RESPIRATION IN RATS

We investigated in rats the effect of 4 wk of hypodynamia on the respi ration of mitochondria isolated from four distinct muscles [soleus, ex tensor digitorum longus, tibial anterior, and gastrocnemius (Gas)] and from subsarcolemmal (SS) and intermyofibrillar (IMF) regions of mixed hindlimb muscles that mainly contained the four cited muscles. With p yruvate plus malate as respiratory substrate, 4 wk of hindlimb suspens ion produced an 18% decrease in state 3 respiration for IMF mitochondr ia compared with those in the control group (P < 0.05). The SS mitocho ndria state 3 were not significantly changed. Concerning the four sing le muscles, the mitochondrial respiration was significantly decreased in the Gas muscle, which showed a 59% decrease in state 3 with pyruvat e + malate (P < 0.05). The other muscles presented no significant decr ease in respiratory rate in comparison with the control group. With su ccinate + rotenone, there was no significant difference in the respira tory rate compared with the respective control group, whatever the mit ochondrial origin (SS, or IMF, or from single muscle). We conclude tha t 4 wk of hindlimb suspension alters the respiration of IMF mitochondr ia in hindlimb skeletal muscles and seems to act negatively on complex I of the electron-transport chain or prior sites. The muscle mitochon dria most affected are those isolated from the Gas muscle.