Thermal injury induces greater resistance to d-tubocurarine in local rather than in distant muscles in the rat

We tested the hypothesis that resistance to d-tubocurarine (dTC) is more in tense in muscles closer to, than distant from, burn, and is related to the expression of immature and total acetylcholine receptors (AChRs). Anestheti zed rats received approximately 4% surface area burn over the tibialis musc le of one leg with the contralateral leg serving as control, or approximate ly 45% of the flank burn, with sham-burned pair fed controls. At 1, 4, 7, o r 14 days later, the 50% effective dose of dTC, membrane AChRs, and messeng er ribonucleic acid (mRNA) that encode the AChR gamma -subunit (AChR gamma -mRNA) were quantified in the tibialis. After the local leg burn, AChRs inc reased at Days 4, 7, and 14, and AChR gamma -mRNA at Days 4 and 7 after bur n. The increased AChR gamma -mRNA correlated with total AChRs (r = 0.82), s uggesting that the up-regulated AChRs may contain the immature isoform. The 50% effective dose of dTC after the local leg burn increased 1.2- to 1.5-f old at all periods and correlated significantly with AChRs (r = 0.54) and A ChR gamma -mRNA (r = 0.57). After the flank burn, resistance was seen at Da y 14 in association with muscle atrophy; AChRs and AChR gamma -mRNA were un altered. The resistance to dTC after a local burn occurs sooner, is more ma rked, and is probably related to both increases and isoform changes in AChR s. The resistance at distant muscles appears unrelated to AChR changes.