Demonstration and quantitation of lactate in oxidative and glycolytic fibers of skeletal muscles

Two peaks consistently arise near 1.3 ppm in $\sp1$H NMR spectroscopic studies of fatiguing skeletal muscles. They are typically 15-20 Hz apart at 300 MHz. Known resonances in this region include lactate, alanine, threonine, and the acyl chain of lipid. From both NMR evidence (COSY, lactate editing, and $\sp{13}$C enrichment) and biochemical evidence (including results of electrical, caffeine or high potassium stimulation, and iodoacetate inhibition of glycolysis), both peaks are identified as lactate.The ratio of intensities of the two lactate methyl peaks in rat soleus, frog semitendinosus, and rat and frog gastrocnemius muscles having differing ratios of glycolytic and oxidative fibers suggests that the peak at 1.29 ppm is associated with glycolytic fibers and the peak at 1.34 ppm is associated with oxidative fibers.Both the CH$\sb3$ and CH protons of lactate experience the same (15-20 Hz) shift in intact muscle; this rules out a chemical binding effect. Oxidative fibers contain much more myoglobin than glycolytic fibers. The appearance of the two sets of lactate peaks in intact muscle can be mimicked by a phantom containing two solutions, one with, and the other without, added myoglobin. The addition of myoglobin shifts every peak in the $\sp1$H spectrum in a myoglobin-concentration and oxygen-dependent manner. One of the two lactate methyl peaks in the muscle spectra also shifts in an oxygen-dependent manner.Additional evidence for a susceptibility effect of myoglobin included: (1) The creatine peak in spectra from muscles containing primarily myoglobin-rich fibers was shifted relative to that in specta from muscles containing primarily fibers with very little myoglobin. (2) All shifts were orientation dependent. That for lactate could be shown to be quantitatively consistently with the theory of the bulk susceptibility effect for an "infinite-cylinder" model.I conclude that the appearance of two lactate peaks in spectra of skeletal muscle results from magnetic susceptibility effects due to myoglobin concentration. The two lactate peaks thus represent separate contributions from glycolytic and oxidative muscle fibers.U of I OnlyETDs are only available to UIUC Users without author permissio