Disparate dysfunction of skeletal muscles located near and distant from burn site in the rat

This study tested the hypotheses that burn-induced change in muscle functio n varies at sites local and distant from burn and is related to changes in expression of acetylcholine receptors (AChRs) and muscle mass. In anestheti zed rats, similar to4% burn was inflicted over the tibialis anterior muscle of one limb. The contralateral leg served as control. In another study, a similar to 45% body surface area burn was produced on the trunk; controls w ere body sham-burned rats. The evoked twitch tensions of tibialis anterior muscles in both legs were measured together with AChR proteins and their tr anscripts. Compared with the contralateral leg, absolute tensions in the bu rned leg declined at days 1, 4, and 7 without loss of muscle mass so that t ension per unit wet muscle mass (specific tension) decreased; at day 14, th e tension decreased with muscle atrophy so that specific tension was unchan ged. Membrane AChRs and/or the immature subunit transcript, AChR gamma mess enger ribonucleic acid (mRNA) increased at days 4, 7, and 14, and both were inversely related to evoked tension (r = .43, P < .01 and r = .01, P < .00 01, respectively). There was a direct correlation between AChR and AChR gam ma mRNA (r = .82, P < .001), suggesting that the upregulated AChRs may cont ain the immature gamma -subunit isoform. After similar to 45% body burn, AC hRs and mRNA did not change and the evoked tensions did not decline, but th ere was relative loss of muscle mass at days 7 and 14 so that specific tens ion increased. Burn trauma initially causes weakness of muscles directly un der the burn, and this weakness may be partially related to increased expre ssion of immature AChRs and later to muscle atrophy. (C) 2001 John Wiley & Sons, Inc.