TYPE-II TO TYPE-I TRANSFORMATION OF CHRONICALLY STIMULATED GOAT LATISSIMUS-DORSI MUSCLE - A HISTOENZYMOLOGICAL, BIOCHEMICAL, BIOENERGETIC, AND FUNCTIONAL-STUDY

Five goat latissimus dorsi muscles (LDM) were submitted to a progressi ve chronic electrostimulation program to reach an integrated understan ding of the fast-to-slow transformation process in large mammals. LDM were regularly sampled and followed during a period of 8 months. Each sample was simultaneously assessed for histoenzymological study, myosi n and LDH isoforms and bioenergetic capacities [NADH dehydrogenase cyt ochrome c oxidoreductase (NADH Cyt c OR), succinate dehydrogenase cyto chrome c oxidoreductase (Succ Cyt c OR), cytochrome c oxidase (Cyt c O x) and LDH]. Such muscles were also tested with and without completion of II to I transformation for their mechanical properties in isometri c and isotonic strain gauge testing. The conversion of fast-to-slow my osin monitored by heavy chain (HC I) and light chain slow component (L C(2)s) began a few days after stimulation and was almost 100% after 10 0 days. The H-LDH isoforms evolved similarly but did not reach 100% co nversion after 200 days. The activity of respiratory chain oxidases in creased within 36 h but to a variable extent and peaked after 32 days, corresponding to a 75% transformation of myosin compared to initial l evels. NADH Cyt c OR, Succ Cyt c OR, and Cyt c Ox, respectively increa sed 10-, 5- and 5-fold. These activities then significantly decreased before the completion of the myofibrillar transformation and reached a plateau with stable activities that remained 2- to 3-fold higher than the unstimulated LDM. LDH activity sharply decreased until day 62 (5- fold) and then plateaued. Functionally, muscle showed a reduced speed of contraction and moderate reduction in power output but had become f atigue-resistant. This study documents the transformation process in l arge mammals and suggests the dynamic relation between workload, aerob ic-anaerobic metabolism and the contractile myofibrillar system.