Influence of tension reduction and peripheral dissection on histologic, biochemical and bioenergetic profiles, and kinetics of skeletal muscle fast-to-slow transformation.

Seven goat latissimus dorsi muscles were submitted to a progressive electrostimulation program through intramuscular electrodes (Medtronic SP5528). Group 1 (n = 3) consisted of muscles stimulated in situ, and group 2 (n = 4), of muscles dissected distally and reinserted on the chest wall with a reduced tension. In group 1, complete fiber switch from type II to I occurred within 60-100 days after the beginning of stimulation, as demonstrated by myosin isoforms and lactate dehydrogenase (LDH) isozymes pattern. Respiratory chain oxidases first increased within 30-70 days after stimulation, then progressively decreased to stabilized values, higher than the basal ones. Total LDH activity showed progressive decrease to one-fifth of the initial value. Morphological analysis confirmed the structural integrity and physical reinforcement of the muscles. In group 2, respiratory chain oxidases showed initial increase followed first by a fast reduction to values less than the starting ones, and then by a slow secondary increase between day 40 and 90. LDH activity displayed a sharp decrease between day 15 and 36. Myosin as well as LDH isoforms showed progressive conversion. This kinetic study suggests a three-phase adaptative evolution of the goat latissimus dorsi submitted to increased workload (group 1): a fast increase (phase I) in oxidative capacities is followed by the development of an efficient contractile machinery (phase II), with subsequent adaptation (phase III) of the terminal chemosmotic enzymes involved in energy production.+2