d3-CaMKII: expression in dilated cardiomyopathy and establishing of a model for functional characterisation

concentration of myosin in single ®bres were studied in elderly subjects. Three groups of two subjects were enrolled in the study: 1) subjects (60±70 years old) who underwent to the replacement of a total knee prosthesis after a period of 3±4 months with the leg immobilized in extended position (el-imm); 2) control adult subjects sampled by needle biopsy (30±40 years old) (yo-ctrl); 3) control aged subjects (60± 70 years old) who underwent to knee surgery for various reasons (elctrl). In immobilized muscles an increase in MHC-2X, a decrease of slow MHC and expression of a developmental MHC isoform, indication of ®bre regeneration, were found. The proportion of hybrid ®bres, i.e. ®bres containing two or more MHC isoforms, increased. As regards type 1 ®bres: cross sectional area (CSA) and speci®c tension (Po/CSA) were found to be lower and maximum shortening velocity (Vo) was found to be higher in el-imm (CSA = 4636 ‹ 2910 (SD) lm, Po/CSA = 20.30 ‹ 15.72 kN/m, n = 25) than in yo-ctrl (CSA = 9793 ‹ 2952 lm, Po/CSA = 40.01 ‹ 21.00 kN/m, n = 118) and el-ctrl (CSA = 6692 ‹ 2979 lm, Po/CSA = 40.62 ‹ 24.56 kN/m, n = 63). CSA and Po/CSA of type 2A ®bres were similarly a€ected; on the contrary, Vo of type 2A ®bres was not statiscally higher following aging and immobilization. Di€erences in Po/CSA between el-imm and the other groups were smaller for 2A than for type 1 ®bres. Myosin concentration in single ®bres was determined by densitometry of myosin electrophoretic bands using samples of known concentration of myosin as standards. Myosin concentration was found signi®cantly lower in ®bres from el-ctrl than in ®bres from yo-ctrl and in ®bres from el-imm than in ®bres from elctrl. This represents a likely explanation of the decrease in Po/CSA observed in aging and following immobilization. Consistently with the decrease in myosin concentration, preliminary analysis of longitudinal sections of muscle bundles by electron microscopy suggested a decrease in myo®brillar density in el-imm in relation to el-ctrl and yo-ctrl.