SINGLE FIBER MYOSIN HEAVY CHAIN DISTRIBUTION WITH MULTIPLE SCLEROSIS

Abstract

PURPOSE: The intent of this investigation was to examine the effects of multiple sclerosis (MS) on human skeletal muscle myosin heavy chain (MHC) distribution. METHODS: Six subjects with MS (age = 44 ± 2 yrs) and seven controls (CON: age = 47 ± 4 yrs) were evaluated. Individual vastus lateralis fibers were analyzed using SDS-PAGE/silver staining to determine MHC distribution. Densitometry was performed on MHC IIa/IIx and I/IIa fibers to determine the relative proportions of MHC I, IIa, and/or IIx. Fiber type and single fiber cross sectional area (CSA) were determined using ATPase histochemistry. Isokinetic concentric and eccentric strength of the knee extensor muscles was evaluated at 1.05 and 3.15 rad/sec. RESULTS: The CON group was 42 and 52% stronger (p < 0.05) than the MS group at concentric velocities of 1.05 and 3.15 rad/sec, respectively. The distribution of total hybrid (I/IIa+I/IIa/IIx+IIa/IIx; MS: 36.0% vs. CON: 25.2%), MHC I (MS: 28.6% vs. CON: 37.2%), and MHC IIa (MS: 28.6% vs. CON: 34.1%) fibers were not different between the two groups. However, the proportion of MHC IIx fibers was greater (p < 0.05) in the MS group (MS: 6.7% vs. CON: 3.5%). MS patients also expressed a greater (p < 0.05) proportion of MHC IIx dominant IIa/IIx fibers (MS: 46.2% vs. CON: 12.7%). No differences were noted in histochemically determined fiber types. Additionally, single fiber CSA, for all fiber types, was not different between the groups. CONCLUSIONS: MHC distribution and ATPase fiber type of the vastus lateralis does not appear to be dramatically altered with MS. Furthermore, strength deficits with MS may not be completely explaned by decreases in fiber CSA. Supported by the National Multiple Sclerosis Society and a Ball State University Graduate Research Award.