DELTA-AMINOLEVULINATE SYNTHASE EXPRESSION IN MUSCLE AFTER CONTRACTIONS AND RECOVERY

The synthesis of haem has been postulated to be a key regulatory step in muscle mitochondrial biogenesis. We examined the expression of delt a-aminolaevulinate synthase (ALAs), the regulatory enzyme of haem meta bolism, in 10 Hz electrically stimulated and non-stimulated control ra t tibialis anterior (TA) muscle. ALAs activity and mRNA levels were me asured at 0, 18 and 48 h of recovery after 3 h of acute stimulation, o r after 7 days of stimulation (3 h/day). ALAs activity in control musc les averaged 7.8 +/- 0. 8 nmol/h per g (n = 30). After 3 h of stimulat ion and during recovery, no change in ALAs activity occurred. ALAs mRN A during the same time was unchanged except at 48 h of recovery, when it increased 1.3-fold above control (P < 0.05), After 7 days of stimul ation, ALAs activity was unchanged at 0 h, but increased at 18 and 48 h of recovery to 2.0- and 1.8-fold above control (P < 0.05). ALAs mRNA was also increaased, but to a level averaging 1.6-fold above control (P < 0.05) at all times, indicating an increased mRNA stability or syn thesis. No change in the haem-containing enzyme cytochrome c oxidase ( CYTOX) activity occurred after 3 h of stimulation in the red section o f the TA. After 7 days of stimulation, the increase in CYTOX activity averaged 1.7-fold above control (P < 0.05) at all times. Thus the indu ction of ALAs during recovery after 7 days was regulated by factors wh ich not only change ALAs mRNA content, but which also affect ALAs mRNA at translational or post-translational steps. This induction occurred despite a 1.7-fold increase in CYTOX, implying that a precursor-produ ct relationship does not always exist.