title: Botulinum toxin-induced paralysis leads to slower myosin heavy chain isoform composition and reduced titin content in juvenile rat gastrocnemius muscle.
abstract: Intramuscular injections of botulinum toxin A (Btx-A) and exercise are used in the treatment of muscle spasticity in children with cerebral palsy. However, little is known about the biological changes within muscle subsequent to Btx-A-induced paralysis and how the combination of Btx-A and exercise might affect the growing muscle. The wet mass, myosin heavy chain (MHC) composition, and titin content of the juvenile rat gastrocnemius muscle were determined 3 weeks after Btx-A injections and subsequent voluntary wheel-running exercise. Btx-A increased the proportion of type IIa (+121%) and IIx (+65%) MHC while decreasing the proportion of type IIb MHC (-51%) and reducing the titin content (-18%). Exercise did not amplify or reduce the changes induced by Btx-A. Thus, we conclude that although the sarcomeric stability of paralyzed muscle might be impaired, moderate mechanical loading does not seem to affect paralyzed muscle protein composition.
authors.affiliation: Department of Sport and Exercise Science, University of Auckland, Private Bag 92019, Auckland Mail Centre, Auckland 1142, New Zealand. k.legerlotz@auckland.ac.nz
authors.forename: Kirsten
authors.initials: K
authors.lastname: Legerlotz
authors.forename: Kenneth G
authors.initials: KG
authors.lastname: Matthews
authors.forename: Christopher D
authors.initials: CD
authors.lastname: McMahon
authors.forename: Heather K
authors.initials: HK
authors.lastname: Smith
mesh_terms: D000367:Age Factors; D000818:Animals; D001835:Body Weight; D019274:Botulinum Toxins, Type A / Q000633:toxicity*; D064211:Connectin; D008297:Male; D009124:Muscle Proteins / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D018995:Myosin Heavy Chains / Q000378:metabolism*; D024461:Myosin Type I / Q000378:metabolism; D009498:Neurotoxins / Q000633:toxicity*; D024507:Nonmuscle Myosin Type IIA / Q000378:metabolism; D024501:Nonmuscle Myosin Type IIB / Q000378:metabolism; D009929:Organ Size; D010243:Paralysis / Q000139:chemically induced* / Q000378:metabolism*; D010805:Physical Conditioning, Animal; D020033:Protein Isoforms / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D064211:Connectin; D009124:Muscle Proteins; D009498:Neurotoxins; D020033:Protein Isoforms; D011494:Protein Kinases; D019274:Botulinum Toxins, Type A; D024461:Myosin Type I; D024507:Nonmuscle Myosin Type IIA; D024501:Nonmuscle Myosin Type IIB; D018995:Myosin Heavy Chains