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Previous studies have suggested the recovery of phosphocreatine (PCr) after exercise is at least second-order in some conditions. Possible explanations for higher-order PCr recovery kinetics include heterogeneity of oxidative capacity among skeletal muscle fibers and ATP production via glycolysis contributing to PCr resynthesis. Ten human subjects (28 [+ or -] 3 yr; mean [+ or -] SE) performed gated plantar flexion exercise bouts consisting of one contraction every 3 s for 90 s (low-intensity) and three contractions every 3 s for 30 s (high-intensity). In a parallel gated study, the sciatic nerve of 15 adult male Sprague-Dawley rats was electrically stimulated at 0.75 Hz for 5.7 min (low intensity) or 5 Hz for 2.1 min (high intensity) to produce isometric contractions of the posterior hindlimb muscles. [[sup.31.]P]-MRS was used to measure relative [PCr] changes, and nonnegative least-squares analysis was utilized to resolve the number and magnitude of exponential components of PCr recovery. Following low-intensity exercise, PCr recovered in a monoexponential pattern in humans, but a higher-order pattern was typically observed in rats. Following high-intensity exercise, higher-order PCr recovery kinetics were observed in both humans and rats with an initial fast component ([tau] < 15 s) resolved in the majority of humans (6/10) and rats (5/8). These findings suggest that heterogeneity of oxidative capacity among skeletal muscle fibers contributes to a higher-order pattern of PCr recovery in rat hindlimb muscles but not in human triceps surae muscles. In addition, the observation of a fast component following high-intensity exercise is consistent with the notion that glycolytic ATP production contributes to PCr resynthesis during the initial stage of recovery. oxidative capacity; fiber types; skeletal muscle; magnetic resonance spectroscopy; nonnegative least-squares analysis

We hypothesized that a period of endurance training would result in a speeding of muscle phosphocreatine concentration ([PCr]) kinetics over the fundamental phase of the response and a reduction in the amplitude of the [PCr] slow component during high-intensity exercise, Six male subjects (age 26 [+ or -] 5 yr) completed 5 wk of single-legged knee-extension exercise training with the alternate leg serving as a control. Before and after the intervention period, the subjects completed incremental and high-intensity step exercise tests of 6-min duration with both legs separately inside the bore of a whole-body magnetic resonance spectrometer. The time-to-exhaustion during incremental exercise was not changed in the control leg [preintervention group (PRE): 19.4 [+ or -] 2.3 min vs. postintervention group (POST): 19.4 [+ or -] 1.9 min] but was significantly increased in the trained leg (PRE: 19.6 [+ or -] 1.6 min vs. POST: 22.0 [+ or -] 2.2 min; P < 0.05). During step exercise, there were no significant changes in the control leg, but end-exercise pH and [PCr] were higher after vs. before training. The time constant for the [PCr] kinetics over the fundamental exponential region of the response was not significantly altered in either the control leg (PRE: 40 [+ or -] 13 s vs. POST: 43 [+ or -] 10 s) or the trained leg (PRE: 38 [+ or -] 8 s vs. POST: 40 [+ or -] 12 s). However, the amplitude of the [PCr] slow component was significantly reduced in the trained leg (PRE: 15 [+ or -] 7 vs. POST: 7 [+ or -] 7% change in [PCr]; P < 0.05) with there being no change in the control leg (PRE: 13 [+ or -] 8 vs. POST: 12 [+ or -] 10% change in [PCr]). The attenuation of the [PCr] slow component might be mechanistically linked with enhanced exercise tolerance following endurance training. [sup.31]phosphorus magnetic resonance spectroscopy; time constant; phosphocreatine dynamics; slow component; fatigue doi: 10.1152/ajpregu.00056.2007

Research was conducted to examine the stimulatory effect of insulin on creatine accumulation in human skeletal muscle. The objectives were to determine whether insulin could stimulate in vivo creatine accumulation in human skeletal muscle, to determine at what plasma insulin concentration a response was evident and to examine whether an insulin-mediated increase in muscle blood blow was associated with any increase in muscle creatine accumulation. Results indicate that plasma creatine concentration was lower at several time points after the administration of insulin.

Research shows that the activity of muscle biochemical phosphocreatine (Pcr) is greater than that of the muscle biochemical creatine (Cr). Experiments designed to study the level of Pcr and Cr in muscle at varying stages of metabolism are described. The role of the muscle biochemical phosphagen as a creatine shuttle is questioned with respect to the results obtained.

The study of K-Cl cotransport in resealed dog red cell ghosts reveals that the cotransport occurs only when creative phosphate is incorporated before resealing. The study indicates that the adenosine triphosphate (ATP) in corporation does not alter the process of cotransportation. The phosphate functions as a substrate for the reactive kinase.

Assay and chromatographic studies indicate that the direct inhibition of actomysin during muscle fatigue does not involve adenosine diphosphate (ADP), as confirmed by a measurement of physiological concentrations of MgADP on single skinned fibers' unloaded shortening velocity and isometric force during fatigue of rabbit fast- and slow-twitch muscles. Changes in creatine concentration using buffer solutions help vary the MgADP levels in the presence of phosphocreatine and creatine kinase and enable ADP and ATP temporal and spatial buffering.

Phosporylcreatine makes up the high-energy pool in human skeletal muscles while phosphagens which are phosphorylated guanidino compounds act as secondary energy sources for intracellular phosphorylation. Nonmammalian phosphagens' distinction from creatine is the lack of a methyl group on the guanidino function and this reflects biochemical imperfection and restraints in evolution. The Mediterranean art of fresco or paintings on freshly plastered walls, such as those done by Florentine Renaissance artist Cimabue, displays immense practical knowledge of inorganic chemistry despite the absence of theoretical basis.

Noninvasive measurements of transmural myocardial metabolites using 3-D [sup.31]P NMR spectroscopy. Am J Physiol Heart Circ Physiol 280: H489-H497, 2001.--A completely noninvasive three-dimensional (3-D) static magnetic field magnitude spatially localized [sup.31]P spectroscopy technique has been developed and applied to study the in vivo canine myocardium at 9.4 T. The technique incorporates both Fourier series windows and selective Fourier transform methods utilizing all three orthogonal gradients for 3-D phase encoding. The number of data acquisitions for each phase-encoding step was weighted according to the Fourier coefficients to define cylindrical voxels. Spatially localized [sup.31]P spectra can be generated for voxels of desired location within the field of view as a postprocessing step. The quality of localization was first demonstrated by using a three-compartment phantom. The technique was then applied to in vivo canine models and yielded [sup.31]P cardiac spectra with an excellent signal-to-noise ratio. The in vivo validation experiments, using an implanted 2-phosphoenolpyruvate-containing marker, demonstrated that the technique is capable of measuring at least two transmural layers of left ventricular myocardium representing the subepicardium and subendocardium. phosphocreatine; ATP; left ventricular hypertrophy three-dimensional; high-energy phosphates