MASS AND FUNCTIONAL-CAPACITY OF REGENERATING MUSCLE IS ENHANCED BY MYOBLAST TRANSFER

Morphology and functional capacity of homotopically transplanted exten sor digitorum longus muscles (EDL) of adult SCID mice that received 1 x 10(6) myoblasts [stably transfected to express nuclear localizing be ta-galactosidase under the control of the myosin light-chain 3F promot er/enhancer] 2 days posttransplantation were evaluated 9 weeks after t ransplantation, to determine whether the injection of exogenous myobla sts had an effect on muscle regeneration. Regenerated muscles that rec eived exogenous myoblasts were compared to similarly transplanted musc les that received (a) no further treatment, or (b) sham injection of t he vehicle (without myoblasts) and to unoperated EDL. Wine weeks after myoblast transfer, myofibers containing donor-derived nuclei could be identified after staining with X-gal solution. Judging from its size and poor functional performance compared to muscles subjected to trans plantation only, sham injection provided a secondary trauma to the reg enerating muscle from which it failed to fully recover. In comparison to the sham-injected muscle, the myoblast-injected muscles weighed 61% more and had 50% more myofibers and 82% more cross-sectional area occ upied by myofibers at the muscles' widest girths. Their absolute twitc h and tetanic tensions were threefold and twofold greater, respectivel y, and their specific twitch and tetanic tensions were 71% and 50% gre ater, respectively, than those of sham-injected muscles. In many param eters, the regenerating muscle subjected to myoblast transfer equaled or exceeded those of muscles that were transplanted only (received onl y one trauma). Absolute twitch and tetanic tensions were 73% and 65% g reater, respectively, and specific twitch tensions of the muscles rece iving myoblasts were 50% greater than forces generated by muscles subj ected to whole-muscle transplantation only. (C) 1997 John Wiley & Sons , Inc.