delta-Aminolaevulinate 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 delta-aminolaevulinate synthase (ALAs), the regulatory enzyme of haem metabolism, in 10 Hz electrically stimulated and non-stimulated control rat tibialis anterior (TA) muscle. ALAs activity and mRNA levels were measured at 0, 18 and 48 h of recovery after 3 h of acute stimulation, or after 7 days of stimulation (3 h/day). ALAs activity in control muscles averaged 7.8 +/- 0.8 nmol/h per g (n = 30). After 3 h of stimulation and during recovery, no change in ALAs activity occurred. ALAs mRNA 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 stimulation, 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 increased, but to a level averaging 1.6-fold above control (P < 0.05) at all times, indicating an increased mRNA stability or synthesis. No change in the haem-containing enzyme cytochrome c oxidase (CYTOX) activity occurred after 3 h of stimulation in the red section of 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 induction of ALAs during recovery after 7 days was regulated by factors which 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-product relationship does not always exist.
Takahashi
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Department of Physical Education, York University, North York, Ontario, Canada.
McCurdy
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Essig
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Hood
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D000624:5-Aminolevulinate Synthetase / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D015152:Blotting, Northern; D004558:Electric Stimulation; D003576:Electron Transport Complex IV / Q000378:metabolism; D015870:Gene Expression; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D009132:Muscles / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
D012333:RNA, Messenger; D003576:Electron Transport Complex IV; D000624:5-Aminolevulinate Synthetase