Mk. Connor et al., Effect of contractile activity on protein turnover in skeletal muscle mitochondrial subfractions, J APP PHYSL, 88(5), 2000, pp. 1601-1606
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.