Cytochrome c transcriptional activation and mRNA stability during contractile activity in skeletal muscle

We evaluated contractile activity-induced alterations in cytochrome c trans criptional activation and mRNA stability with unilateral chronic stimulatio n (10 Hz, 3 h/day) of the rat tibialis anterior (TA) muscle for 1, 2, 3, 4, 5, and 7 days (n = 3-11/group). Transcriptional activation was assessed by direct plasmid DNA injection into the TA with a chloramphenicol acetyltran sferase (CAT) reporter gene linked to 326 bp of the cytochrome c promoter. Cytochrome c mRNA in stimulated muscles increased by 1.3- to 1.7-fold above control between 1 and 7 days. Cytochrome c protein was increased after 5 d ays of stimulation to reach levels that were 1.9-fold higher than control b y 7 days. Cytochrome c mRNA stability, determined with an in vitro decay as say, was greater in stimulated TA than in control between 2 and 4 days, lik ely mediated by the induction of a cytosolic factor. In contrast, cytochrom e c transcriptional activation was elevated only after 5 days of stimulatio n when mRNA stability had returned to control levels. Thus the contractile activity-induced increase in cytochrome c mRNA was due to an early increase in mRNA stability, followed by an elevation in transcriptional activation, leading to an eventual increase in cytochrome c protein levels.