Non-P-i buffer capacity and Initial phosphocreatine breakdown and resynthesis kinetics of human gastrocnemius/soleus muscle groups using 0.5 s time-resolved P-31 MRS at 4.1 T

High-time-resolution (0.5 s) P-31 MRS has been used to evaluate the initial phosphoreatine (PCr) breakdown and resynthesis kinetics, to calculate the non-P-i/non-bicarbonate buffer capacity (beta(non-P/non-bicarb)), and to ca lculate the constant relating the change in intracellular pH to the muscle' s H+ efflux rate (lambda), The slope of PCr vs time demonstrates that a slo pe calculated using the first 10 s of recovery underestimates initial PCr r ecovery rates by up to 56%. A 1-2 s time window is needed to produce a slop e that is statistically equivalent to the slope measured using a 0.5 s time window (p = 0.008, one-way RM-ANOVA, Student-Newman-Keuls multiple compari son test). In addition, there was no delay or acceleration in PCr recovery after a 90 s maximum voluntary contraction (MVC) in normal subjects. This d emonstrates that. oxidative metabolism is occurring at the end of a 90-s MV C in normal individuals. Fitting recovery data has determined that beta(non -Pi/non-bicarb) = 24.3 +/- 5.4 slyke (mmol/L/pH unit) and that lambda = 0.1 29 +/- 0.077 mM/(ph s) for human gastrocnemius/soleus muscle. beta(non-Pi/n on-bicarb) is in agreement with measurements in cat biceps, cat soleus and rat gastrocnemius muscles. Copyright (C) 1999 John Wiley & Sons, Ltd.