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Denervation Alters Myosin Heavy Chain Expression And Contractility Of Developing Rat Diaphragm Muscle

Gary C. Sieck, Wen-Zhi Zhan

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We hypothesized that unilateral denervation (DNV) of the rat diaphragm muscle (Diam) in neonates at postnatal day 7 (D-7) alters normal transitions of myosin heavy chain (MHC) isoform expression and thereby affects postnatal changes in maximum specific force (Po) and maximum unloaded shortening velocity ( V o). The relative expression of different MHC isoforms was analyzed electrophoretically. With DNV at D-7, expression of MHCneo in the Diam persisted, and emergence of MHC2X and MHC2B was delayed. By D-21 and D-28, relative expression of MHC2A and MHC2Bwas reduced in DNV compared with control (CTL) animals. Expression of MHCneo also reappeared in adult Diam by 2–3 wk after DNV, and relative expression of MHC2B was reduced. At each age, Po was reduced and V o was slowed by DNV, compared with CTL. In CTL Diam, postnatal changes in Po and V o were associated with an increase in fast MHC isoform expression. In DNV Diam, no such association existed. We conclude that, in the Diam, DNV induces alterations in both MHC isoform expression and contractile properties, which are not necessarily causally linked.