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

Abstract

In 1H NMR spectroscopic studies of fatiguing skeletal muscles, two peaks consistently arise near 1.3 ppm, typically 15-20 Hz apart at 300 MHz. From a variety of NMR and biochemical evidence, both peaks are identified as lactate. Both the CH3 and CH protons of lactate experience the same shift in intact muscle; this rules out chemical bonding or complexation. 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 paramagnetic myoglobin in the oxidative fibers. Phantom studies, as well as oxygen, temperature, field, and orientation dependence of the muscle spectra are all consistent with an explanation based upon bulk magnetic susceptibility. It is concluded that the two lactate peaks represent separate contributions from glycolytic and oxidative muscle fibers.

The carnosine C‐2 proton's chemical shift reports intracellular pH in oxidative and glycolytic muscle fibers

“…Based on Arú s and Barany's work (14), a total of four peaks would be seen in this region of the spectrum: one imino proton from the imidazole ring of histidine, the H-2 and H-8 protons of ATP and ADP, and the carnosine C-2 proton. Indeed, in homogenates from exercised frog gastrocnemii, Shen (28) identified these four peaks in the 8.0 -8.6 ppm region of the 1 H spectrum. This supports the hypothesis that following exercise, whole muscles contain two physical compartments with two distinct pH values.…”

“…These procedures were approved by the Laboratory Animal Care Committee of the University of Illinois at UrbanaChampaign, and were described previously (17). Briefly, 24 pairs of gastrocnemius muscles were dissected from Rana pipiens (Kons Scientific, Germantown, WI) and bathed in a modified Ringer's solution (10 mM Tris, 105 mM NaCl 2 , 2.0 mM KCl, 2.0 mM MgCl 2 , 2.5 mM CaCl 2 , pH 7.2 at 21°C).…”

“…Twelve of the muscle pairs were exposed to 0.5 mM IAA in Ringer's solution for ϳ3 hr prior to the start of the NMR analyses. The muscles were mounted in an experimental chamber as described by Shen et al (17), which allowed for length adjustment, direct electrical stimulation of the muscle, and force measurements via a cantilevered strain gauge placed at the top of the magnet. The muscles were maintained at 14°C in the magnet, and the rest tension was 100 g/g wet weight (w.w.) of tissue.…”

Intracellular acidification and volume increases explain R2 decreases in exercising muscle

“…NaCN (2.0 mM) exposure began ϳ2 h prior to the onset of exercise; after 1 h of NaCN exposure, oxygen consumption ceases in these muscles. The muscles were mounted in the experimental chamber described by Shen et al (16), which allows length adjustment, electrically stimulated contractions, and mechanical measurements. The chamber was placed in the magnet, and the muscles were maintained at 14°C.…”

“…The muscle exercise and force recording protocols were those described by Shen et al (16) (60 maximal isometric fused tetani elicited via 23 mAmp ⅐ cm -2 , 10-ms square waves delivered at 40 Hz for 1 s/min). In some studies (N ϭ 4), force was recorded by a cantilevered strain gauge placed at the top of the magnet.…”