title: Resistance to rocuronium of rat diaphragm as compared with limb muscles.
abstract: BACKGROUND
  Skeletal muscles are composed of different muscle fiber types. We investigated the different potency to rocuronium among diaphragm (DIA), extensor digitorum longus (EDL), and soleus (SOL) in vitro as well as to investigate the differences of acetylcholine receptors (AChRs) among these three typical kinds of muscles.
  
  
  METHODS
  The isolated left hemidiaphragm nerve-muscle preparations, the EDL sciatic nerve-muscle preparations, and the SOL sciatic nerve-muscle preparations were established to evaluate the potency to rocuronium. Concentration-response curves were constructed and the values of IC50 were obtained. The density of AChRs at the end plate and the number of AChRs per unit fiber cross fiber area (CSA), AChR affinity for muscle relaxants were evaluated.
  
  
  RESULTS
  The concentration-twitch tension curves of rocuronium were significantly different. The curves demonstrated a shift to the right of the DIA compared with the EDL and SOL (P < 0.01), whereas no significant difference was observed between EDL and SOL (P > 0.05). IC50 was significantly largest in DIA, second largest in SOL, and smallest in EDL (P < 0.05). The number of AChRs per unit fiber CSA was largest in DIA, second largest in EDL, and smallest in SOL (P < 0.01 or P < 0.05). The DIA showed the lowest affinity of the AChRs, whereas the SOL showed the highest affinity.
  
  
  CONCLUSIONS
  The resistance to rocuronium of DIA compared with EDL and SOL was verified. The DIA was characterized by the largest number of AChRs per unit fiber CSA and the lowest affinity of the AChRs. Although compared with SOL, EDL was proved to have larger number of AChRs per unit fiber CSA and the lower affinity of the AChRs. These findings may be the mechanisms of different potency to rocuronium in DIA, EDL, and SOL. The results of the study could help to explain the relationship between different composition of muscle fibers and the potency to muscle relaxants. Extra caution should be taken in clinical practice when monitoring muscle relaxation in anesthetic management using different muscles.
authors.affiliation: Department of Anesthesiology, The Affiliated First People's Hospital, Shanghai Jiaotong University, Shanghai, China.
authors.forename: Lina
authors.initials: L
authors.lastname: Huang
authors.affiliation: Department of Anesthesiology, The Affiliated First People's Hospital, Shanghai Jiaotong University, Shanghai, China.
authors.forename: Meirong
authors.initials: M
authors.lastname: Yang
authors.affiliation: Department of Anesthesiology, The Affiliated First People's Hospital, Shanghai Jiaotong University, Shanghai, China.
authors.forename: Lianhua
authors.initials: L
authors.lastname: Chen
authors.affiliation: Department of Anesthesiology, The Affiliated First People's Hospital, Shanghai Jiaotong University, Shanghai, China. Electronic address: lishitongpaper@gmail.com.
authors.forename: Shitong
authors.initials: S
authors.lastname: Li
mesh_terms: D000732:Androstanols / Q000494:pharmacology*; D000818:Animals; D003964:Diaphragm / Q000187:drug effects*; D004351:Drug Resistance; D005121:Extremities; D006801:Humans; D008297:Male; D009045:Motor Endplate / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D018656:Muscle Fibers, Fast-Twitch / Q000187:drug effects; D018657:Muscle Fibers, Slow-Twitch / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D018482:Muscle, Skeletal / Q000187:drug effects; D003473:Neuromuscular Nondepolarizing Agents / Q000494:pharmacology*; D017207:Rats, Sprague-Dawley; D011950:Receptors, Cholinergic / Q000378:metabolism; D000077123:Rocuronium; D012584:Sciatic Nerve / Q000187:drug effects*
chemical_list: D000732:Androstanols; D003473:Neuromuscular Nondepolarizing Agents; D011950:Receptors, Cholinergic; D000077123:Rocuronium
keywords: Diaphragm; Extensor digitorum longus; Potency; Rocuronium; Soleus