Altered expression of myosin heavy chain in the vastus lateralis muscle inpatients with COPD

This study was designed to further characterize peripheral skeletal muscle alterations in patients with chronic obstructive pulmonary disease (COPD) a nd to evaluate the possible relationship between myosin heavy chain (MyoHC) isoform expression and exercise tolerance in these individuals. MyoHC composition from biopsy of the vastus lateralis muscle was examined i n 12 COPD patients (forced expiratory volume in one second (FEV1)=31+/-9% p redicted, peak oxygen consumption (V'O-2)=15+/-4 mL.kg(-1).min(-1)) and 10 age-matched normal male subjects (peak V'(O2)=20+/-15 mL.kg(-1).min(-1)). The proportion of MyoHC type I was smaller in COPD than in normals (27+-17% ve,sns 41+/-9%, p<0.05) with an increase in MyoHC type IIa (51 +/- 15% ver sus 39+/-93%, p<0.05) and the proportion of MyoHC type IIx being comparable between both groups. A significant relationship was found between peak V'O -2 mL.kg(-1).min(-1) and FEV1% pred (r=0.91, p<0.0001) and the percentage o f MyoHC type I (r=0.61, p=0.016), In stepwise multiple regression, only FEV 1% pred was found to be a significant determinant of peak V'O-2 (p<0.0001). This variable explained 83% of the total variance of peak V'O-2. In summary, this study shon ed considerable modifications in the phenotypic expression of the myosin heavy chain in the vastus lateralis muscle in pat ients with chronic obstructive pulmonary disease. An independent effect of myosin heavy chain expression on exercise capacity was not found. These res ults suggest that chronic inactivity and muscle deconditioning may not be t he sole factors explaining peripheral muscle dysfunction in patients with c hronic obstructive pulmonary disease.