A study of the differences in sensitivities to rocuronium between the facial muscles and limb skeletal muscles and facial muscle-evoked myogenic potential monitoring

Abstract

Objective To test the differences in sensitivities to rocuronium between facial nerve- and somatic nerve-innervated muscles, investigate whether the different muscle sensitivities to rocuronium are related to the nicotinic acetylcholine receptor (nAChR) subunits, and explore the relationship between the differences in nAChR expression among these muscles and the agrin/low-density lipoprotein receptor-related protein 4 (Lrp4)/muscle-specific kinase (MuSK) and neuregulin1 (NRG1)/epidermal growth factor receptor (ErbB) signaling pathways. Methods The left sided orbicularis oris and gastrocnemius were obtained from male Sprague-Dawley rats. Their pharmacodynamic responses to rocuronium were detected in vitro, and the values of 50% inhibitory concentration (IC50) were obtained according to dose-response curves. The levels of nAChR α1, β1, δ, e, and γ subunits were assessed by immunofluorescence. The mRNA and protein amounts of agrin, Lrp4, MuSK, matrix metalloproteinase (MMP3), NRG1, ErbB2, ErbB3, and ErbB4 were assessed by reverse transcription polymerase chain reaction(RT-PCR) and Western blot. Results The IC50 value of the orbicularis oris to rocuronium was significantly higher than that of the gastrocnemius. The orbicularis oris presented a higher density of nAChR subunits in unit cross-sectional area than the gastrocnemius. The mRNA and protein amounts of NRG1β,ErbB2, ErbB3, and ErbB4 were higher in the orbicularis oris than those in the gastrocnemius. Meanwhile, no differences were observed in the mRNA or protein levels of agrin, Lrp4, MuSK, or MMP3. Conclusions Facial nerve-innervated muscle is less sensitive to skeletal muscular relaxants than somatic nerve-innervated muscle, which may be related to the density of nAChR subunits in unit cross-sectional area. The higher expression of nAChR subunits in the orbicularis oris may be related to the NRG1/ErbB signaling pathway, rather than the agrin/Lrp4/MuSK signaling pathway. Key words: Facial muscles; Skeletal muscles; Facial nerve; Evoked myogenic potentials; Rocuronium; Nicotinic acetylcholine receptor