Correlation of contractile function recovery with acetylcholine receptor changes in a rat muscle flap model

The aim of this study was to investigate the correlation between contractile function recovery and changes of acetylcholine receptors (AChR) in a transferred muscle flap following reinnervation. Orthotopic transfer of the gracilis muscle flap with repair of its nerve was performed bilaterally in 48 rats. The rats were randomly divided into six experimental groups based on the time intervals for assessments (1, 4, 5, 10, 20, and 30 weeks). Sixteen gracilis muscle samples from eight rats without surgery were used as the controls. In each group, muscle contractile force and weight were measured (n = 16). The AChR numbers (n = 8) and subunits (epsilon and gamma) mRNA (n = 8) were examined using [(125)I]-alpha-bungarotoxin and fluorescent quantitative-PCR. The results showed the AChR numbers in the muscle flap increased from 4 to 20 weeks after reinnervation and correlated with recovery of the tetanic contraction force. However, correlation between the increase of AChR number with the specific tension (peak contractile force normalized to wet muscle weight) was only found from 4 to 10 weeks postoperatively. The expression of gamma-subunit mRNA increased at the early period after flap transfer and then decreased rapidly, whereas the epsilon-subunit mRNA recovered gradually since fourth week postoperatively. A small amount of gamma-subunit mRNA could still be detected at 30 weeks after surgery. In conclusion, following reinnervation of the transferred muscle flap, the contractile functional recovery is partially correlated to increase of the AChRepsilon. Our findings may provide evidence for further study of improving muscle function in functional reconstruction by targeting the AChR.