Myosin heavy chain isoform transformation in single fibres from m. vastus lateralis in spinal cord injured individuals: effects of long-term functional electrical stimulation (FES).

The myosin heavy chain (MHC) composition of single fibres from m. vastus lateralis of five spinal- cord-injured (SCI) individuals was analysed by Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) before, and after 6 and 12 months of functional electrical stimulation (FES)-training, administrated for 30 min three times per week. Prior to FES training 37.2% of the fibres contained only MHC IIB, 21.2% only MHC IIA, and 40.7% co-expressed MHC IIA and MHC IIB. After 6 months of FES-training the number of fibres containing only MHC IIB was reduced to 2.6% (P < 0.05), the number of fibres containing only MHC IIA was increased to 44.3% (P < 0.05), and the number of fibres co-expressing MHC IIA and MHC IIB was 50.9% (ns). After 12 months almost all fibres (91.2%, P < 0.05) contained only MHC IIA. The number of fibres containing only MHC IIB was 2.3% and the fibres co-expressing MHC IIA and IIB had decreased to 4.6% (P < 0.05). The amount of fibres containing only MHC I never exceeded 0.5%. Likewise, the number of fibres co-expressing MHC I and MHC IIA was below 2% throughout the study period. In total, the MHC composition of 1596 single fibres was determined. This study shows that FES-training of paralysed human skeletal muscle administrated over a prolonged period of time, can lead to a marked switch in MHC expression from about equal amounts of MHC IIA and MHC IIB to an almost total dominance of MHC IIA.