title: [The impairment of excitation-contraction (E-C) coupling in myasthenia gravis].
abstract: We have developed a new novel method to assess the function of excitation-contraction (E-C) coupling in patients with myasthenia gravis (MG). In our procedure, masseteric compound muscle action potential (CMAP) and mandibular movement-related potentials (MRP) were recorded simultaneously after stimulating the trigeminal motor nerve with a needle electrode. The E-C coupling time (ECCT) was calculated by the latency difference between CMAP and MRP. Bite force was measured using a pressure-sensitive sheet. Our serial studies demonstrate that masseteric E-C coupling is impaired in some MG patients, and functional recovery of E-C coupling contributes at least in part to the increase in bite force after treatment. We also reveal that presence of anti-RyR antibodies is associated with significantly prolonged masseteric ECCT compared to absence of the antibodies in MG, and tacrolimus (FK506) induces ECCT shortening accompanying clinical improvement within 2 weeks. These results indicate the contribution of anti-ryanodine receptor (RyR) antibody to E-C coupling impairment, and the early effect of tacrolimus as a pharmacological enhancement of RyR function to improve E-C coupling in MG. In further studies, the present method may be applied to assess the post-tetanic potentiation of E-C coupling in human skeletal muscles.
authors.affiliation: Department of Neurology, Sapporo Medical University School of Medicine.
authors.forename: Tomihiro
authors.initials: T
authors.lastname: Imai
mesh_terms: D001323:Autoantibodies / Q000276:immunology; D056966:Excitation Contraction Coupling / Q000502:physiology*; D006801:Humans; D008406:Masseter Muscle / Q000503:physiopathology; D009157:Myasthenia Gravis / Q000503:physiopathology*; D019837:Ryanodine Receptor Calcium Release Channel / Q000276:immunology
chemical_list: D001323:Autoantibodies; D019837:Ryanodine Receptor Calcium Release Channel