Anaerobic Metabolism During High Intensity Exercise

1. Anaerobic Metabolism During High Intensity Exercise

2. Various Roles for Anaerobic Metabolism • Essential when the demand for ATP is greater than can be provided by aerobic metabolism • At the onset of high-intensity exercise • At maximal O2 consumption

3. The onset of High Intensity Exercise • Anaerobically derived ATP may contribute 80-90 % of the total • O2 is in short supply until cardiovascular system can meet demands

4. Near Maximal O2 Uptake • Near maximal O2 uptake, increases in workload elicit greater contribution from anaerobic sources • Since aerobic metabolism is maximal, the only other source of ATP is from non-oxidative sources

5. Anaerobic Contribution Decreases as Exercise Progresses • 30 s • 80 % anaerobic/20 % aerobic • 60-90 s • 45 % anaerobic/55 % aerobic • 120-180 s • 30 % anaerobic/70 % aerobic

6. Insert fig 1.2

7. Insert Fig 1.1

8. Sources of Anaerobic ATP • CP or PCr degradation • Endogenous ATP • Glycolysis

9. PCr Degradation Creatine PhosphoKinase PCr + ADP + H+ ATP + Cr

10. Glycolysis • Glycogen + 3 ADP + H+3 ATP + 2 lactate + 2 H+ • Can use this relationship to determine ATP provision from glycolysis during intense exercise • Take a post exercise muscle biopsy and multiply [La+] by 1.5 • Must also take into account lactate that leaves muscle

11. Adenosine Phosphorylation Adenylate Kinase 2 ADP  ATP + AMP • creates an ATP, but also leaves an AMP

12. Deamination AMP + H+ IMP + NH4+ AMPDeaminase • Conversion of AMP to IMP is irreversible • Prevents buildup of AMP • in conjunction with Adenylate Kinase prevents accumulation of ADP

13. [ATP]/[ADP] Ratio • Important because it determines free energy • Hi [ATP]/[ADP] allows ATP to be converted to ADP more easily • If this happens, there is more free energy • Lo [ATP]/[ADP] • ATPADP more difficult • Less free energy

14. How do you keep the ratio high? • Keep making ATP from ADP • Also, Adenylate Kinase • ADP + ADP  ATP + AMP • But AMP can go back to ADP

15. So • Deamination converts ADP to IMP and removes loitering ADPs • Adenylate Kinase and AMP deaminase work together to prevent AMP and ADP buildup

16. Why do we want to keep ratio high? • To maintain control of energy flow • We must generate ATP, but if ADP or AMP accumulate we lose control of metabolism

17. Timing of Anaerobic Pathways

18. Traditional “Serial Metabolism” • PCr degradation immediate and only source of ATP supply in first 10 s • When PCr depleted glycolysis begins • No overlap of two pathways • Recent evidence argues against this

19. PCr Degradation • PCr degradation is indeed instantaneous • Biopsies after 1.28 s of electrical stimulation show PCr breakdown

20. Glycolysis Also Instantaneous • Elevated [La+] reported after 10 s cycling 110 % VO2max • Although no resting sample taken (Saltin et al., Jacobs et al.) • Other studies have shown [La+] after only 6 s, and PCr stores were not depleted after 6 or 10 s

21. Rates of Anaerobic Metabolism • Anaerobic ATP must be provided at very high rate • Power outputs of 2-4 times VO2max can be attained for short periods • Even though anaerobic pathways provide less ATP per mole of substrate than oxidative pathways

22. Insert Table 1.2

23. Rate Continued • 0-10 s - ~6.0 – 9.0 mmol ATP/kg dm/s • Combined for PCr and glycolysis • 30 s – PCr ~ 1.6 and glycolysis ~4.4 mmol/kg dm/s • Assuming 25 % releas of lactate, ~5.8 for glycolysis

24. Insert fig 1.4

25. Take Home • Highest rates of ATP provision from PCr and glycolysis 0-10 s • From 10 – 30 s PCr stores are depleted • Glycolytic rate ~ 50 % of intitial 10 s • Glycolytic rate of ATP provision during 30s maximal exercise, 3-4 times > PCr

26. Direct Measurement of Anaerobic ATP Provision • Insert Table 1.3

27. Problems Associated with Measuring Anaerobic ATP Provision • Must take pre and post-exercise biopsies • Must account for lactate release from muscle • Arterial and venous blood sampling • If not, exhaustive exercise or…. • Spriet et al. and closed circulation

28. Glycolysis • During intense exercise bouts ~3 min, glycolysis provides ~ 80 % total anaerobic ATP • Glycolysis is activated more quickly than aerobic metabolism • provides ATP at a higher rate • Can provide more ATP than PCr degradation

29. Glucose from where? • Glucose can come from blood or glycogen • During short-intense exercise, primarily from glycogen • Uptake of glucose cannot meet glycolytic demand

30. GLUT proteins

31. Regulation • Accumulation of G-6-P inhibits glucose phosphorlation • Primary points of regulation are PHOS and PFK

32. Why does G-6-P inhibit glucose phosphorylation? • Low level of glycolytic flux • Glycolysis isn’t moving very fast • Must not need G-6-P • That glucose can be stored as glycogen instead of being utilized for glycolysis

33. PHOS regulation • PHOS = glycogen phosphorylase • The enzyme responsible for breakdown of glycogen to glucose • Removes one glucose at a time by adding Pi (phosphorylating)

34. Insert fig 12.2 from Houston

35. PHOS cont’d • Km of PHOS for glycogen very low (1-2 mM) • Means that PHOS has high affinity for glycogen • This means PHOS can function effectively even at low glycogen concentrations

36. More PHOS • Previous exercise can affect glycogenolytic rate relative to glycogen concentration • For example during afternoon practice following morning practice.. • If glycogen stores are low, glycogenolysis will be reduced • Higher glycogen stores will result in higher relative glycogenolysis

37. Insert fig 1.5

38. Pi and PHOS regulation • Phosphorylation of PHOS (pretty redundant eh?) results in conversion of forms • b is inactive form • a is active form • Phosphorylation converts b form to a • Implications for activity???

39. At rest 10-20% of PHOS in a form • Conversion from b to a doesn’t necessarily mean increased glycogenolysis • Free Pi also needs to be available for elevated glycogenolysis to occur

40. Calcium activates PHOS kinase • Phosphorylation of PHOS (again) results from PHOS kinase • PHOS kinase activated by elevations in intracellular [Ca2+]

41. Why would you want to tie PHOS to intracellular [Ca 2+]?? • With E/C coupling Ca2+ released from sarcoplasmic reticulum • Intracellular [Ca2+] elevated drastically and rapidly • Therefore glycogenolysis is tied closely to muscular contraction

42. Acidosis hinders PHOS acitivity • Conversion of PHOS b to a is depressed under acidic conditions • After repeated bouts of interval cycling, decreased activation of glycogenolysis related to increasing muscle acidity (Spriet et al.) • Although activity was still reduced in a second bout 1 hour after the first, where H+ had recovered

43. Phosphofructokinase (PFK) regulation • Most important regulator of PFK activity is ATP • ATP can bind to PFK at two sites and alter its activity • Binds to catalytic site with high affinity • Can also bind to allosteric site

44. PFK cont’d • Binding to the allosteric site inhibits activity • So,… when [ATP] in the cell is high, PFK will be inhibited • no need for glycolysis, plenty of ATP • H+ can enhance ATP affinity for allosteric site • Provides feedback inhibition

45. Some other proposed modulators • Inhibitors • Citrate • Phosphoglycerate • Phophoenolpyruvate • Mg2+

46. Promoters • AMP and ADP • Pi • NH4+ • Fructose –2,6 diphosphate

47. Citrate • Probably not a major factor during short, intense exercise • Aerobic metabolism does not contribute greatly until later (>30 s) • Citrate probably does not accumulate within the 30-60 s time frame

48. Promoters • ADP and AMP will accumulate rapidly at the onset of anaerobic exercise • Breakdown of PCr • H+ may be reduced at the onset of exercise • Removing the ATP induced inhibition

49. Conclusion • PFK regulation is obviously a complicated matter • During exercise many of the promoters (ADP,AMP, Pi, and NH4+) will accumulate • ATP will be reduced, but H+ should also rise • There may be unidentified factros which help maintain the awkward balance of promotion and inhibition during intense exercise