Adaptive responses to creatine loading and exercise in fast-twitch rat skeletal muscle

Abstract

We investigated the effects of chronic creatine loading and voluntary running (Run) on muscle fiber types, proteins that regulate intracellular Ca2+, and the metabolic profile in rat plantaris muscle to ascertain the bases for our previous observations that creatine loading results in a higher proportion of myosin heavy chain (MHC) IIb, without corresponding changes in contractile properties. Forty Sprague-Dawley rats were assigned to one of four groups: creatine-fed sedentary, creatine-fed run-trained, control-fed sedentary, and control-fed run-trained animals. Proportion and cross-sectional area increased 10% and 15% in type IIb fibers and the proportion of type IIa fibers decreased 11% in the creatine-fed run-trained compared with the control-fed run-trained group (P < 0.03). No differences were observed in fast Ca2+-ATPase isoform SERCA1 content (P > 0.49). Creatine feeding alone induced a 41% increase (P < 0.03) in slow Ca2+-ATPase (SERCA2) content, which was further elevated by 33% with running (P < 0.02). Run training alone reduced parvalbumin content by 50% (P < 0.05). By comparison, parvalbumin content was dramatically decreased by 75% (P < 0.01) by creatine feeding alone but was not further reduced by run training. These adaptive changes indicate that elevating the capacity for high-energy phosphate shuttling, through creatine loading, alleviates the need for intracellular Ca2+ buffering by parvalbumin and increases the efficiency of Ca2+ uptake by SERCAs. Citrate synthase and 3-hydroxyacyl-CoA dehydrogenase activities were elevated by run training (P < 0.003) but not by run training + creatine feeding. This indicates that creatine loading during run training supports a faster muscle phenotype that is adequately supported by the existing glycolytic potential, without changes in the capacity for terminal substrate oxidation.

The effects of hypoventilation disorder on physiological and biochemical properties of the hindlimb muscles

“…This may have been a result of an elevation of the fatigue index due to fast to slow transition. Generally, fast-to-slow transition has been reported to be induced by electric stimulation at a relatively low frequency (6,14) and endurance exercise (11,12), but in our experiment it was induced by hypoventilation disorder. This alteration is thought to be caused by inaction of physical activity.…”

Creatine loading elevates the intracellular phosphorylation potential and alters adaptive responses of rat fast-twitch muscle to chronic low-frequency stimulation

“…Two groups consumed, ad libitum, a solution of 5% dextrose (vehicle) (Fisher Scientific, Fairlawn, N.J., USA); one of those groups received 10 days of CLFS applied to the left hind limb on days 11-20 (dextrose-CLFS, n = 6), while the second received a sham operation of the left hind limb (dextrose-control, n = 5). Throughout the study the third and fourth groups consumed, ad libitum, a solution of 1% Cr (Createam, NutraSense Inc., Shawnee Mission, Kans., USA) that was sweetened with 5% dextrose to increase palatability and maximise Cr intake (Gallo et al 2006(Gallo et al , 2008. Ten days of CLFS was applied to the left hind limb of the third group (creatine-CLFS, n = 7) and the fourth group received a sham operation of the left hind limb (creatine-control, n = 6).…”

“…TA muscles were analysed for TCr (Gallo et al 2008). Neutralised perchloric acid (PCA) extracts of freeze-dried, powdered TA muscles were added to 1 mol/L nitric acid, boiled for 40 min, cooled to 4°C, and cleared by centrifugation (12 000g for 5 min, 4°C).…”

“…Based on those collective observations, we recently investigated whether increasing the cellular energy potential within rat plantaris, by long-term Cr loading, would attenuate fast-to-slow phenotypic transitions typically associated with long-term voluntary wheel running of an intermittent, high-frequency nature (Gallo et al 2006(Gallo et al , 2008. In those studies, prolonged muscle Cr loading attenuated running-induced fast-to-slow fibre type transitions.…”

“…Although Cr feeding induced a 20% increase in total muscle Cr content (TCr), a corresponding increase in the IPP was not detected in whole-muscle extracts. This was attributed to the phasic, highfrequency nature of voluntary run training facilitating preferential Cr uptake into heavily recruited type IIB fibres (Gallo et al 2008). Because the IIB population represented only 23% of all fibres in rat plantaris, the maximum increase in whole-muscle IPP was limited to 4.6%.…”