Anaerobic Metabolism During Anaerobic Metabolism During High Intensity ExerciseHigh Intensity Exercise

Various Roles for Anaerobic Various Roles for Anaerobic MetabolismMetabolism

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

The onset of High Intensity The onset of High Intensity ExerciseExercise

Anaerobically derived ATP may contribute 80-90 % of the total

– O2 is in short supply until cardiovascular system can meet demands

Near Maximal ONear Maximal O22 Uptake 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

Anaerobic Contribution Anaerobic Contribution Decreases as Exercise Decreases as Exercise

ProgressesProgresses30 s

– 80 % anaerobic/20 % aerobic

60-90 s

– 45 % anaerobic/55 % aerobic

120-180 s

– 30 % anaerobic/70 % aerobic

Insert fig 1.2Insert fig 1.2

Insert Fig 1.1Insert Fig 1.1

Sources of Anaerobic ATPSources of Anaerobic ATP

CP or PCr degradation

Endogenous ATP

Glycolysis

PCr DegradationPCr Degradation

Creatine PhosphoKinase

PCr + ADP + H+ ATP + Cr

GlycolysisGlycolysis

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

Adenosine PhosphorylationAdenosine Phosphorylation

Adenylate Kinase

2 ADP ATP + AMP

• creates an ATP, but also leaves an AMP

DeaminationDeamination

AMP + H+ IMP + NH4+

AMP Deaminase

• Conversion of AMP to IMP is irreversible

• Prevents buildup of AMP

• in conjunction with Adenylate Kinase prevents accumulation of ADP

[ATP]/[ADP] Ratio[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] – ATPADP more difficult

– Less free energy

How do you keep the ratio How do you keep the ratio high?high?

Keep making ATP from ADP

Also, Adenylate Kinase

– ADP + ADP ATP + AMP

– But AMP can go back to ADP

SoSo

Deamination converts ADP to IMP and removes loitering ADPs

Adenylate Kinase and AMP deaminase work together to prevent AMP and ADP buildup

Why do we want to keep ratio Why do we want to keep ratio high?high?

To maintain control of energy flow

We must generate ATP, but if ADP or AMP accumulate we lose control of metabolism

Timing of Anaerobic PathwaysTiming of Anaerobic Pathways

Traditional “Serial Metabolism”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

PCr DegradationPCr Degradation

PCr degradation is indeed instantaneous

Biopsies after 1.28 s of electrical stimulation show PCr breakdown

Glycolysis Also InstantaneousGlycolysis 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

Rates of Anaerobic Rates of Anaerobic MetabolismMetabolism

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

Insert Table 1.2Insert Table 1.2

Rate ContinuedRate 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

Insert fig 1.4Insert fig 1.4

Take HomeTake 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

Direct Measurement of Direct Measurement of Anaerobic ATP ProvisionAnaerobic ATP Provision

Insert Table 1.3

Problems Associated with Measuring Problems Associated with Measuring Anaerobic ATP ProvisionAnaerobic 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

GlycolysisGlycolysis

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

Glucose from where?Glucose from where?

Glucose can come from blood or glycogenDuring short-intense exercise, primarily

from glycogenUptake of glucose cannot meet glycolytic

demand

GLUT proteinsGLUT proteins

RegulationRegulation

Accumulation of G-6-P inhibits glucose phosphorlation

Primary points of regulation are PHOS and PFK

Why does G-6-P inhibit glucose Why does G-6-P inhibit glucose phosphorylation?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

PHOS regulationPHOS regulation

PHOS = glycogen phosphorylase

The enzyme responsible for breakdown of glycogen to glucose

Removes one glucose at a time by adding Pi (phosphorylating)

Insert fig 12.2 from HoustonInsert fig 12.2 from Houston

PHOS cont’dPHOS 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

More PHOSMore 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

Insert fig 1.5Insert fig 1.5

Pi and PHOS regulationPi 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???

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

Calcium activates PHOS Calcium activates PHOS kinasekinase

Phosphorylation of PHOS (again) results from PHOS kinase

PHOS kinase activated by elevations in intracellular [Ca2+]

Why would you want to tie PHOS to Why would you want to tie PHOS to intracellular [Ca intracellular [Ca 2+2+]??]??

With E/C coupling Ca2+ released from sarcoplasmic reticulum

Intracellular [Ca2+] elevated drastically and rapidly

Therefore glycogenolysis is tied closely to muscular contraction

Acidosis hinders PHOS acitivity 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

Phosphofructokinase (PFK) Phosphofructokinase (PFK) regulationregulation

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

PFK cont’dPFK 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

Some other proposed Some other proposed modulatorsmodulators

Inhibitors

– Citrate

– Phosphoglycerate

– Phophoenolpyruvate

– Mg2+

Promoters

– AMP and ADP

– Pi

– NH4+

– Fructose –2,6 diphosphate

CitrateCitrate

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

PromotersPromoters

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

ConclusionConclusion

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