Shaking up glycolysis: Sustained, high lactate flux during aerobic rattling

Substantial ATP supply by glycolysis is thought to reflect cellular anoxia in vertebrate muscle. An alternative hypothesis is that the lactate generat ed during contraction reflects sustained glycolytic ATP supply under well-o xygenated conditions. We distinguished these hypotheses by comparing intrac ellular glycolysis during anoxia to lactate efflux from muscle during susta ined, aerobic contractions. We examined the tailshaker muscle of the rattle snake because of its uniform cell properties, exclusive blood circulation, and ability to sustain rattling for prolonged periods. Here we show that gl ycolysis is independent of the O-2 level and supplies one-third of the high ATP demands of sustained tailshaking, Fatigue is avoided by rapid H+ and l actate efflux resulting from blood flow rates that are among the highest re ported for vertebrate muscle. These results reject the hypothesis that glyc olysis necessarily reflects cellular anoxia. Instead, they demonstrate that glycolysis can provide a high and sustainable supply of ATP along with oxi dative phosphorylation without muscle fatigue.