Contractile properties of single muscle fibers in myotonic dystrophy

✍ Scribed by Lisa S. Krivickas; Tor Ansved; Dongwon Suh; Walter R. Frontera

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 239 KB
• Volume: 23
• Category: Article
• ISSN: 0148-639X
• DOI: 10.1002/(sici)1097-4598(200004)23:4<529::aid-mus11>3.0.co;2-y

✦ Synopsis

Muscle fiber contractile dysfunction in myotonic dystrophy (MD) is poorly understood. We biopsied the tibialis anterior of two symptomatic and three asymptomatic subjects (aged 21-31 years) with the MD mutation. Biopsies were freeze dried. A total of 103 single muscle fibers were activated with Ca ++ , allowing maximal force measurements and specific force (SF) estimates. The slack test was performed to calculate maximum unloaded shortening velocity (V o ). The myosin heavy chain composition of each fiber was determined using sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Type I and IIA fibers of all subjects had reduced SF when compared with healthy control subjects (P < 0.001). In addition, the type I fibers of symptomatic subjects generated less SF than those of asymptomatic subjects (P < 0.001). Type I fibers from asymptomatic and symptomatic subjects did not differ in V o , but V o was lower than in control subjects (P < 0.001). There was no significant difference in V o of type IIA fibers from symptomatic, asymptomatic, and control subjects. These results indicate that the MD mutation leads to a diminished force-generating capacity of the myofilaments in both symptomatic and asymptomatic individuals. The results further suggest that reduction in forcegenerating capacity at the cellular level develops prior to clinical weakness.