title: Linear dependence of muscle phosphocreatine kinetics on oxidative capacity.
abstract: The influence of muscle oxidative capacity on phosphocreatine (PCr) changes during and after stimulation was examined in the superficial (fast-twitch) section of rat gastrocnemius muscles. Muscle mitochondrial enzymes were increased in one group of rats by 8-10 wk of training on a running wheel (to a final regimen of 50 min/day at 38 m/min, 5 days/wk) and decreased in another group by chemical thyroidectomy [0.025% methimazole (MMI) in drinking water for 8 wk]. After these treatments, muscle citrate synthase activity was 179 and 29%, respectively, of that in corresponding control groups. Muscle PCr and pH were measured by 31P-nuclear magnetic resonance spectroscopy before, during, and after 8 min of isometric twitch stimulation at 0.33 Hz (MMI) or 0.75 Hz (trained) and 2 Hz. There was a significant linear correlation (r = 0.84, P < 0.01) between the rate constant for PCr recovery after submaximal stimulation (0.33 or 0.75 Hz) and citrate synthase activity. Within the control groups, there was a significant correlation (r = 0.72, P < 0.01) between the rate constant for PCr recovery and intracellular pH at the end of stimulation. The results are quantitatively consistent with linear/quasilinear models of respiratory control by the cytoplasmic free energy of ATP hydrolysis but not with respiratory control by cytoplasmic ADP.
authors.affiliation: Department of Physiology, Michigan State University, East Lansing 48824, USA.
authors.forename: A T
authors.initials: AT
authors.lastname: Paganini
authors.forename: J M
authors.initials: JM
authors.lastname: Foley
authors.forename: R A
authors.initials: RA
authors.lastname: Meyer
mesh_terms: D000818:Animals; D002950:Citrate (si)-Synthase / Q000378:metabolism; D004558:Electric Stimulation / Q000379:methods; D007700:Kinetics; D008297:Male; D009119:Muscle Contraction; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism*; D010101:Oxygen Consumption; D010725:Phosphocreatine / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D010725:Phosphocreatine; D002950:Citrate (si)-Synthase