title: Attenuation of myosin light chain phosphorylation and posttetanic potentiation in atrophied skeletal muscle.
abstract: Previously we have demonstrated that the absence of staircase potentiation in atrophied rat gastrocnemius muscle is accompanied by a virtual absence of phosphorylation of the regulatory light chains (R-LC) of myosin. It was our purpose in the present study to determine if posttetanic potentiation and corresponding R-LC phosphorylation were also attenuated in disuse-atrophied muscles. Two weeks after a spinal hemisection (T12), twitch and tetanic contractile characteristics were measured in situ in control, sham-treated and atrophied (hemisected) muscles. Posttetanic potentiation 20 s after a 2 s tetanic contraction (200 Hz) was depressed in atrophied muscles (128.7 +/- 2.6%; mean +/- SEM) when compared to sham-treated (149.9 +/- 2.4%) and control (142.9 +/- 2. 7%) muscles. Atrophied muscles demonstrated a significant increase in R-LC phosphorylation from rest (0.05 +/- 0.04 moles of phosphate/mole of R-LC) to posttetanic conditions (0.21 +/- 0.03 moles of phosphate/mole of R-LC), and less phosphorylation than control and sham-treated muscles (0.43 +/- 0.06 and 0.49 +/- 0.03 moles of phosphate/mole of R-LC, respectively) after tetanic stimulation. The preservation of the potentiation-phosphorylation relationship in atrophied muscles is consistent with the hypothesis that R-LC phosphorylation may be the principal mechanism for twitch potentiation.
authors.affiliation: Faculty of Kinesiology and Medicine, University of Calgary, Calgary, Alberta, T2N 1N4, Canada.
authors.forename: L A
authors.initials: LA
authors.lastname: Tubman
authors.forename: D E
authors.initials: DE
authors.lastname: Rassier
authors.forename: B R
authors.initials: BR
authors.lastname: MacIntosh
mesh_terms: D000818:Animals; D003714:Denervation; D004558:Electric Stimulation; D005260:Female; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000378:metabolism / Q000503:physiopathology*; D009133:Muscular Atrophy / Q000209:etiology / Q000378:metabolism / Q000503:physiopathology*; D018994:Myosin Light Chains / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000502:physiology
chemical_list: D018994:Myosin Light Chains