OBSERVATION AND QUANTITATION OF LACTATE IN OXIDATIVE AND GLYCOLYTIC FIBERS OF SKELETAL-MUSCLES

In H-1 NMR spectroscopic studies of fatiguing skeletal muscles, two pe aks consistently arise near 1.3 ppm, typically 15-20 Hz apart at 300 M Hz. From a variety of NMR and biochemical evidence, both peaks are ide ntified as lactate. Both the CH3 and CH protons of lactate experience the same shift in intact muscle; this rules out chemical bonding or co mplexation. The ratio of intensity of the two methyl peaks varies with muscle type and suggests a correlation with oxidative and glycolytic fiber populations. The shift can be accounted for by the presence of p aramagnetic myoglobin in the oxidative fibers. Phantom studies, as wel l as oxygen, temperature, field, and orientation dependence of the mus cle spectra are all consistent with an explanation based upon bulk mag netic susceptibility. It is concluded that the two lactate peaks repre sent separate contributions from glycolytic and oxidative muscle fiber s.