Denervation alters myosin heavy chain expression and contractility of developing rat diaphragm muscle

We hypothesized that unilateral denervation (DNV) of the rat diaphragm musc le (Dia,) 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 (P-o) and maximum unloaded shortening vel ocity (V-o). The relative expression of different MHC isoforms was analyzed electrophoretically. With DNV at D-7, expression of MHCneo in the Dia(m) p ersisted, and emergence of MHC2X and MHC2B was delayed. By D-21 and D-28, r elative expression of MHC2A and MHC2B was reduced in DNV compared with cont rol (CTL) animals. Expression of MHCneo also reappeared in adult Dia(m) by 2-3 wk after DNV, and relative expression of MHC2B was reduced. At each age , P-o was reduced and V-o was slowed by DNV, compared with CTL. In CTL Dia( m), postnatal changes in P-o and V-o were associated with an increase in fa st MHC isoform expression. In DNV Dia(m), no such association existed. We c onclude that, in the Dia(m), DNV induces alterations in both MHC isoform ex pression and contractile properties, which are not necessarily causally lin ked.