Lactate efflux from fatigued fast-twitch muscle fibres of Xenopus laevis under various extracellular conditions

• Published in: The Journal of physiology Vol. 481; no. Pt 1; pp. 139 - 147
• Main Authors: Nagesser, A S, van der Laarse, W J, Elzinga, G
• Format: Journal Article
• Language: English
• Published: England The Physiological Society 15-11-1994
• Subjects: Animals; Extracellular Space; Female; Lactates - metabolism; Muscle Fatigue - physiology; Muscle Fibers, Fast-Twitch - physiology; Space life sciences; Xenopus laevis
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.1994.sp020425

1. Isolated, fast-twitch, low-oxidative muscle fibres from the iliofibularis muscle of Xenopus laevis were fatigued by intermittent
tetanic stimulation at 20 degrees C in different Ringer solutions and the amount of lactate released was determined. 2. The
rate of lactate efflux was constant during 10 min of intermittent stimulation while lactate in the fibres accumulated, and
lactate efflux was not hampered by an unstirred layer surrounding the isolated muscle fibre. 3. The rate of lactate efflux
at extracellular pH 7.2 was the same as that at pH 7.8, but depended on the type of buffer used; the highest efflux rate (mean
+/- S.E.M., 7.4 +/- 2.2 mumol min-1 (g dry weight)-1, n = 8) was observed in bicarbonate-buffered Ringer solution. This rate
was about 2.5 times higher than the rate in phosphate-buffered Ringer solution (2.9 +/- 1.3 mumol min-1 (g dry weight)-1,
n = 8), indicating that lactate-bicarbonate exchange is the most important route for lactate extrusion in vivo. 4. The highest
rate of lactate efflux corresponds to a rate of glycolytic ATP production which is only about 30% of the oxidative rate of
ATP production (calculated from the maximum rate of oxygen consumption determined previously). 5. In the presence of 5 mM
alpha-cyano-4-hydroxycinnamate (CHC) the lowest lactate efflux rate (1.5 +/- 0.6 mumol min-1 (g dry weight)-1, n = 16) was
found. This rate was independent of the composition of the Ringer solution. Assuming that 5 mM CHC completely inhibits lactate
transporters in the sarcolemma, the rate of lactate efflux in the presence of 5 mM CHC can be explained by passive diffusion,
but only if most lactate is extruded via the T-tubules.