DIFFERENTIAL TITIN ISOFORM EXPRESSION IN HUMAN SKELETAL-MUSCLE

Mammalian skeletal muscle expresses al least two isoforms of the cytos keletal protein titin (connectin; MW approximate to 3000 kDa). These i soforms are associated with different passive force curves, and thus m ay affect physical performance. To study the distribution of titin and its possible influence on performance in humans, muscle biopsies were obtained from 15 males ((X) over bar +/- SE; age = 25.4 +/- 2.9 years , height = 177.7 +/- 1.8 cm, weight = 76.5 +/- 2.2 kg). Two biopsies w ere obtained on separate occasions from both the right and left vastus lateralis, and one biopsy each from the lateral head of the right gas trocnemius and the right soleus, with ail biopsies handled identically . Fibre type analyses were performed via mATPase histochemistry. Expre ssion of titin and myosin heavy chain isoforms were determined by SDS- PAGE. Titin bands in the resulting gels were highly repeatable and wer e verified by migration patterns, as well as Western blot analysis. Tw o groups of subjects were identified: group 1 (n = 10) expressed only one titin isoform (titin-l) in all biopsies, and group 2 (n = 5) expre ssed two titin isoforms (titin-1 and titin-2) in all biopsies. No sign ificant differences (P > 0.05) between groups were observed for percen tage fibre types, percentage fibre type areas, fibre type cross-sectio nal areas, and percentage myosin heavy chain expression when comparing individual muscles, sampling limes or bilateral comparisons. This is the first report of differential titin isoform expression in healthy, mature human skeletal muscle, but it is not clear why this occurs or w hat influence this may have on performance.