Effect of contractile activity on protein turnover in skeletal muscle mitochondrial subfractions

To determine the role of intramitochondrial protein synthesis (PS) and degr adation (PD) in contractile activity-induced mitochondrial biogenesis, we e valuated rates of [S-35]methionine incorporation into protein in isolated r at muscle subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondria. Rat es of PS ranged from 47 to 125% greater (P < 0.05) in IMF compared with SS mitochondria. Intense, acute in situ contractile activity (10 Hz, 5 min) of fast-twitch gastrocnemius muscle resulted in a 50% decrease in PS (P < 0.0 5) in SS but not IMF mitochondria. Recovery, or continued contractile activ ity (55 min), reestablished PS in SS mitochandria. In contrast, PS was not affected in either SS or IMF mitochondria after prolonged (60-min) contract ile activity in the presence or absence of a recovery period. PD was not in fluenced by 5 min of contractile activity in the presence or absence of rec overy but was reduced after 60 min of contractions followed by recovery. Ch ronic stimulation (10 Hz, 3 h/day, 14 days) increased muscle cytochrome-c o xidase activity by 2.2-fold but reduced PS in IMF mitochondria by 29% (P < 0.05; n = 4). PS in SS mitochondria and PD in both subfractions were not ch anged by chronic stimulation. Thus acute contractile activity exerts differ ential effects on protein turnover in IMF and SS mitochondria, and it appea rs that intramitochondrial PS does not limit the extent of chronic contract ile activity-induced mitochondrial biogenesis.