Table 2

Increased HLa accumulation in the absence of O2-limitation

1. a.  HLa production depends on a competition for pyruvate and NADH between LDH and the NADH shuttles (malate-aspartate and glycerol-phosphate) and the pyruvate transporter (MCT)
 b.  High activity of LDH and Keq of pyruvate to lactate reaction guarantees HLa production particularly with increasing glycolytic rate
2.  Phosphorylase is activated by increased work rate probably due to ↑ [Ca2+], ↑ [Pi], and ↑ [AMP]; this increases glycolytic rate ⇒ ↑ HLa production
3.  With increased exercise intensity; [ATP] ↓, [ADP] ↑, [AMP] ↑, [Pi] ↑, and [ammonia] ↑ ⇒ phosphofructokinase (PFK) activation and ↑ HLa production
4.  ↑ [Ca2+] may act in a feed-forward manner to activate phosphorylase and PFK independently of metabolic feedback
5.  Sympathoadrenal activity increases with work rate—epinephrine activates phosphorylase and thereby ↑ glycolysis and HLa production
6.  Sympathoadrenal activity also causes vasoconstriction and ↓ blood flow to liver, kidney, and inactive muscle ⇒ ↓ HLa oxidation and removal
7.  Fast twitch fiber recruitment increases HLa production
8.  HLa production exceeds removal ⇒ ↑ muscle and blood [HLa]
  • [Modified with permission from ref. 21 (Copyright 1996, Oxford University Press).]