Chronic stimulation-induced changes in mitochondria and performance in rat skeletal muscle

Chronic low-frequency (10-Hz) electrical stimulation was used to investigate mitochondrial biogenesis in rat tibialis anterior muscle. Succinate dehydrogenase and citrate synthase were used as mitochondrial enzymes, and cardiolipin (CL) was used as a phospholipid index of the inner membrane. Stimulation was via the peroneal nerve (24 h/day) for 1, 2, 3, 5, 7, 10, 14, 21, and 28 days (n = 3-9 rats/day). After each period, endurance performance was evaluated in situ. The contralateral side (CON) served as control nonstimulated muscle. Endurance performance gradually improved after 5 days of stimulation to approximately twofold higher than CON muscle beyond 10 days. Succinate dehydrogenase activity rose to 2.4-fold above CON muscle (4.8 +/- 0.2 U/g; n = 54) by 10 days (half time = 6.1 days) and then remained constant. Citrate synthase demonstrated a similar change. The improved performance with stimulation was correlated (r = 0.61, P < 0.05) to these increases in enzyme activities. CL concentration increased from CON (0.35 +/- 0.02 mumol/g; n = 30) to 3.6- and 3.8-fold above CON at 10 and 14 days (half time = 4.2 days). This increase in CL was greater (P < 0.05) than for either enzyme during the same period. These data are consistent with a model of mitochondrial membrane biogenesis in which enzyme proteins are inserted into a presynthesized lipid bilayer.