Energía(/(ATP( Aminoácidos( - vet.unicen.edu.ar · Fuentes(de(ATP(durantela...

21
MÚSCULO Trabajo –> Movimiento Termogénesis Reserva (depósito) de aminoácidos (Nitrógeno) EsqueléGco (ME) Contracción de las miofibrillas Síntesis y degradación de proteínas (recambio proteico) Equilibrio iónico (Na+, K+) de membranas Energía / ATP Crecimiento > Retención de proteínas (Nitrógeno) Aminoácidos Liso (ML) Cardíaco (MC) Depósito (USO LOCAL) de glucosa como glucógeno Síntesis y degradación de glucógeno Glucosa OXIDACIÓN DE CARBOHIDRATOS Y LÍPIDOS

Transcript of Energía(/(ATP( Aminoácidos( - vet.unicen.edu.ar · Fuentes(de(ATP(durantela...

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MÚSCULO  Trabajo  –>  Movimiento  

Termogénesis  

Reserva  (depósito)  de  aminoácidos  (Nitrógeno)  

EsqueléGco  (ME)  

Diversidad  histológica  y  en  la  fisiología  de  la  contracción    

Contracción  de  las  miofibrillas  

Síntesis  y  degradación  de  proteínas  (recambio  proteico)  

Equilibrio  iónico  (Na+,  K+)  de  membranas  

Energía  /  ATP  

Crecimiento  -­‐>  Retención  de  proteínas  (Nitrógeno)  

Aminoácidos  

Liso  (ML)  Cardíaco  (MC)   Depósito  (USO  LOCAL)  de  glucosa  como  glucógeno  

Síntesis  y  degradación  de  glucógeno  

Glucosa  

OXIDACIÓN  DE  CARBOHIDRATOS  Y  LÍPIDOS  

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Capacidad  oxidaGva:  Gpos  de  fibras  musculares  y  músculos  

LENTAS,  OXIDATIVAS  

RÁPIDAS,  OXIDATIVAS  Y  GLICOLÍTICAS  

RÁPIDAS,  GLICOLÍTICAS  

FIBRAS  

LENTOS  ROJOS  

RÁPIDOS  ROJOS  

RÁPIDOS  BLANCOS  

MÚSCULOS   O2  

O2  

ESPECIES  

CABALLOS    Y  OVEJAS  VACAS  Y  CONEJOS  

CERDOS  

POLLOS  

O2  

O2  

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GLUCOSA  

ÁCIDOS  GRASOS  

CUERPOS  CETÓNICOS  ACETATO  

Krebs   H+   H+  

ATP  

CO2   CALOR  

Recambio  proteico  

Temblor  

Movimiento  Postura  

Mantenimiento  celular  

Glucogenogénesis  Glucogenolisis  

CALOR  

CALOR  

Aporte  O2  ≥  Requerimientos  O2  (ME,  ML,  MC)  

G6P  

GLUCÓGENO  

PIRUVATO   LACTATO  

 

ATP  

Movimientos    de  alta  demanda  de  energia  por  unidad  de  Gempo  

Aporte  O2  <  Requerimientos  O2  (ME)  

O2  

CALOR  

GLUCÓGENO  MUSCULAR  LACTATO  (MC)  

HÍGADO  

GLUCOSA  

CORAZÓN  

CO2  

ATP  

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PIR  

G6P  

GLUCÓGENO  

LP-­‐TAG   AGL  ACETATO  GLUCOSA  

AGL  

CETÓNICOS  

GLUT4  

AGL  ACIL-­‐CoA  

ACoA  

ACIL-­‐CoA  

ATP  

FOx  

H+  

ADP  

H++  e-­‐  

 ATP  

ATP  

AMP  G6P  

PIR  

Krebs  AOA  PIR  

GLUCÓGENO  

LAC  

ATP  

LAC  

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[ATP]      EN  MÚSCULO     <  1  SEGUNDO  DE  CONTRACCIÓN  

CreaGna-­‐P  

ADP  

CreaGna  

ATP  CREATINA-­‐P  

25  mM  

ATP  4mM  

∆G’=  -­‐12  KJ/mol  

¿Cuál  es  el  sustrato  que  manGene  la  contracción  en  los  primeros  momentos?  

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449

16 CHAPTER

O U T L I N E

16.1 Glycolysis Is an Energy-Conversion Pathway in Many Organisms

16.2 The Glycolytic Pathway Is Tightly Controlled

16.3 Glucose Can Be Synthesized from Noncarbohydrate Precursors

16.4 Gluconeogenesis and Glycolysis Are Reciprocally Regulated

Glycolysis and Gluconeogenesis

The first metabolic pathway that we encounter is glycolysis, an ancient pathway employed by a host of organisms. Glycolysis is the sequence of

reactions that metabolizes one molecule of glucose to two molecules of pyruvate with the concomitant net production of two molecules of ATP. This process is anaerobic (i.e., it does not require O 2 ) because it evolved before substantial amounts of oxygen accumulated in the atmosphere. Pyruvate can be further processed anaerobically to lactate ( lactic acid fermentation ) or ethanol ( alco-holic fermentation ) . Under aerobic conditions, pyruvate can be completely oxidized to CO 2 , generating much more ATP, as will be described in chapters 17 and 18. Figure 16.1 shows some possible fates of pyruvate pro-duced by glycolysis.

Because glucose is such a precious fuel, metabolic products, such as pyruvate and lactate, are salvaged to synthesize glucose in the process of gluconeogenesis. Although glycolysis and gluconeogenesis have some enzymes in common, the two pathways are not simply the reverse of each other. In particular, the highly exergonic, irreversible steps of glycolysis are bypassed in gluconeogenesis. The two pathways are reciprocally regulated so that glycolysis and gluconeogenesis do not take place simultaneously in the same cell to a significant extent.

Usain Bolt sprints to a win in the 200-meter finals at the Olympics in London in 2012. Glucose metabolism can generate the ATP to power muscle contraction. During a sprint, when the ATP needs outpace oxygen delivery, as would be the case for Bolt, glucose is metabolized to lactate. When oxygen delivery is adequate, glucose is metabolized more efficiently to carbon dioxide and water.   [Christophe Karaba/epa/Corbis.]

A. Low O2 (last seconds of a sprint)

B. Normal (long slow run)

Muscle fiber

Glucose Pyruvate

CytoplasmMitochondrion

ATP

ATP

ALactate

BCO2 + H2O

Glycolysis

GlycolysisDerived from the Greek stem glyk-, “sweet,” and the word lysis, “dissolution.”

CreaGna  ADP  

ATP

Contracción  muscular  

A  

B  

C  

DP-­‐CreaGna  

O2  

Fuentes  de  ATP  durante  la  contracción  muscular  en  el  ejercicio.      

Glucosa   Piruvato   Lactato  

Citoplasma  Mitocondria  

Fibra  muscular  

Glicólisis  AGL  

D

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Fuentes  de  ATP  durante  la  contracción  muscular  en  el  ejercicio.      

The amount of ATP in muscle suffices to sustain contractile activity for less than a second. Creatine phosphate in vertebrate muscle serves as a res-ervoir of high-potential phosphoryl groups that can be readily transferred to ADP. Indeed, we use creatine phosphate to regenerate ATP from ADP every time that we exercise strenuously. This reaction is catalyzed by cre-atine kinase . Creatine kinase

Creatine phosphate 1 ADP ! ATP 1 creatine

At pH 7, the standard free energy of hydrolysis of creatine phosphate is 2 43.1 kJ mol 2 1 ( 2 10.3 kcal mol 2 1 ), compared with 2 30.5 kJ mol 2 1 ( 2 7.3 kcal mol 2 1 ) for ATP. Hence, the standard free-energy change in forming ATP from creatine phosphate is 2 12.6 kJ mol 2 1 ( 2 3.0 kcal mol 2 1 ), which corresponds to an equilibrium constant of 162.

Keq 5

[ATP][creatine][ADP][creatine phosphate]

5 e2¢G89y2.47 5 e12.6y2.47 5 162

In resting muscle, typical concentrations of these metabolites are [ATP] 5 4 mM, [ADP] 5 0.013 mM, [creatine phosphate] 5 25 mM, and [cre-atine] 5 13 mM. Because of its abundance and high phosphoryl-transfer potential relative to that of ATP, creatine phosphate is a highly effective phosphoryl buffer. Indeed, creatine phosphate is the major source of phosphoryl groups for ATP regeneration for a runner during the first 4  seconds of a 100-meter sprint. The fact that creatine phosphate can replenish ATP pools is the basis of the use of creatine as a dietary supple-ment by athletes in sports requiring short bursts of intense activity. After the creatine phosphate pool is depleted, ATP must be generated through metabolism (Figure 15.7).

TABLE 15.1 Standard free energies of hydrolysis of some phosphorylated compounds

Compound kJ mol21 kcal mol21

Phosphoenolpyruvate 261.9 214.81,3-Bisphosphoglycerate 249.4 211.8Creatine phosphate 243.1 210.3ATP (to ADP) 230.5 2 7.3Glucose 1-phosphate 220.9 2 5.0Pyrophosphate 219.3 2 4.6Glucose 6-phosphate 213.8 2 3.3Glycerol 3-phosphate 2 9.2 2 2.2

FIGURE 15.7 Sources of ATP during exercise. In the initial seconds, exercise is powered by existing high-phosphoryl-transfer compounds (ATP and creatine phosphate). Subsequently, the ATP must be regenerated by metabolic pathways.

ATP

Creatine phosphateAnaerobic

metabolism(Chapter 16)

Aerobic metabolism(Chapters 17 and 18)

Seconds Hours

Ener

gy

Minutes

43115.2 ATP: Currency of Free Energy

EnergÍa  para  la  contracción  

Fosfato  de  CreaWna  

Metabolismo  aeróbico  

Metabolismo  anaeróbico  

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GLUT4  

INSULINA  y  EJERCICIO  

Ejercicio  

GLUT4  Insulin  

Na   Na   Na  

CAPTACIÓN  DE  GLUCOSA  

DESCANSO  

POSTPRANDIAL  

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GLUCÓGENO  

GS  

G6P  

PIR  

ACoA  

CO2  

FFK  

PDH  

AGL  ACIL-­‐CoA  

ACIL-­‐CoA  

ATP  

FOx  

H+  

ADP  

H++  e-­‐  

 ATP  Krebs  

MAL-­‐CoA  ACoA  

ACAC2  

-­‐  

-­‐  

ICDH  

+  

DESCANSO  

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GLUCÓGENO  

GS  

G6P  

PIR  

ACoA  

CO2  

FFK  

PDH  

AGL  ACIL-­‐CoA  

ACIL-­‐CoA  

ATP  

FOx  

H+  

ADP  

H++  e-­‐  

 ATP  Krebs  

MAL-­‐CoA  ACoA  

ACAC2  

-­‐  

-­‐  

EJERCICIO  

-­‐  

ICDH  

t/D  

ATP/ADP  

t/D  

+  

t/D  

+  

+  

+  

+  

EJERCICIO  

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GLUCÓGENO  

GS  

G6P  

PIR  

ACoA  

CO2  

FFK  

PDH  

AGL  ACIL-­‐CoA  

ACIL-­‐CoA  

ATP  

FOx  

H+  

ADP  

H++  e-­‐  

 ATP  Krebs  

MAL-­‐CoA  ACoA  

ACAC2  

-­‐  

-­‐  

EJERCICIO  

-­‐  

ICDH  

t/D  

ATP/ADP  

t/D  

+  

t/D  

+  

+  

+  ADRENALINA  

+  

+  

ADRENALINA  

+  

EJERCICIO  

LIPÓLISIS  

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GLUCÓGENO  

GS  

G6P  

PIR  

ACoA  

CO2  

FFK  

PDH  

AGL  ACIL-­‐CoA  

ACIL-­‐CoA  

ATP  

FOx  

H+  

ADP  

H++  e-­‐  

 ATP  Krebs  

MAL-­‐CoA  ACoA  

ACAC2  

-­‐  

INSULINA  

-­‐  

ICDH  

+  

+  

LUEGO  DEL  EJERCICIO  +  CONSUMO  DE  CARBOHIDRATOS  

-­‐  

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GLUCÓGENO  

GS  

G6P  

PIR  

ACoA  

CO2  

FFK  

PDH  

AGL  ACIL-­‐CoA  

ACIL-­‐CoA  

ATP  

FOx  

H+  

ADP  

H++  e-­‐  

 ATP  Krebs  

MAL-­‐CoA  ACoA  

ACAC2  

-­‐  

-­‐  

ICDH  

PERÍODO  POSTASORTIVO  

GLUCAGON  

+  

LIPÓLISIS  

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100  

Descanso  Liviano  

25%  VO2  max  2-­‐3  min  

Contribución  a  la  oxidación  (%)  

50  

AGL   CETÓNICOS   GLUCOSA  

Liviano  25%  VO2  max  

60  min  

Moderado  65%  VO2  max  

60  min  

Intenso  85%  VO2  max  

30  min  

Intenso  85%  VO2  max  60-­‐120  min  

OXIDACIÓN  DE  LÍPIDOS  Y  CARBOHIDRATOS  DURANTE  EL  EJERCICIO  EN  HUMANOS  

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J.F. Hocquette et al. / Livestock Production Science 56 (1998) 115–143 119

Glucose is extracted by muscle through facilitated Within resting muscles, glucose can follow severaldiffusion via transmembrane glucose transporters, metabolic pathways: (1) direct oxidation, (2) gly-mainly the insulin-sensitive isoform (glucose trans- colysis to L-lactate, which is then released to theporter No. 4: GLUT4). The rate-limiting role of circulation, (3) glycogen synthesis, which constitutesglucose transport in glucose homeostasis and a major fate of glucose (Pethick, 1984) and (4) fattyglycogen deposition within muscle cells was demon- acid synthesis, in particular in intramuscular adiposestrated by several in vivo and in vitro approaches tissue (Smith and Crouse, 1984). At steady state, the(for review, see Hocquette et al., 1996a). The glucose uptake by muscle (corrected for lactate andmajority of GLUT4 is inside the cell in the basal pyruvate output) if completely oxidized could con-state, from where it can be rapidly translocated to the tribute 31–57% of resting muscle energy expenditureplasma membrane following stimulation either by in sheep (Pethick, 1984, Fig. 3), 31–41% in humansinsulin or by exercise. The regulation of GLUT4 (Elia et al., 1988; Mandarino et al., 1993) and

14expression and activity in skeletal muscles differs probably more in pigs (Lindsay, 1981). Using C-among cattle, goats (Hocquette et al., 1995), sheep glucose tracers, only 18–26% of extracted glucose in(Sasaki, 1994), pigs (Hocquette et al., 1996b) and sheep is promptly oxidized to CO with the remain-2rats (for reviews, see Girard et al., 1992; Hocquette der of the glucose carbon probably passing throughet al., 1996a). The recent cloning of GLUT4 probes pools which turnover more slowly (glycogen, pro-in pigs (Chiu et al., 1994), sheep (Bennett et al., tein) before being oxidized. Glycogen can be mobil-1995) and cattle (Abe et al., 1997) will allow further ized either for glycolysis or for oxidative catabolism.understanding of the regulation of glucose transport Glycolysis is controlled by PFK activity, which isin domestic animals. inhibited by an excess of ATP or lactate (Regen et

Fig. 3. The maximum potential contribution of metabolites to oxidation in resting or exercising hindlimb skeletal muscle of sheep, assumingcomplete oxidation. The absolute utilisation of nutrients was calculated using data based on arterio–venous measurements after havingaccounted for recycled metabolites. Then, the respective contribution (in %) of each energy-yielding substrate was estimated as the ratio ofnutrient use to total oxygen consumption on an energy basis. The estimates represent the mean of the exercise period (Pethick, 1984; Pethicket al., 1987; Harman, 1991; Harman and Pethick, 1994).

USO  DE  SUSTRATOS  ENERGÉTICO  POR  EL  MÚSCULO  EN  OVEJAS  

AGL  

CETÓNICOS  

ACETATO  

GLUCOSA  

NIVEL  DE  EJERCICIO  

Descanso

Contribución  a  la  oxidación  (%)  

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(103 mol of ATP at best) are insufficient to provide the 150 mol of ATP needed for this grueling event. Much larger quantities of ATP can be obtained by the oxidation of fatty acids derived from the breakdown of fat in adipose tissue, but the maximal rate of ATP generation is slower yet than that of glycogen oxidation and is more than 10-fold slower than that with creatine phosphate. Thus, ATP is generated much more slowly from high-capacity stores than from limited ones , accounting for the different velocities of anaerobic and aerobic events. Fats are rapidly consumed in activities such as distance running, explaining why extended aerobic exercise is beneficial for people who are insulin resistant.

Is i t possible to determine the contribution of each fuel as a function of exercise intensity? The percentage contribution of each fuel can be measured with the use of a respirometer, which measures the respiratory quotient (RQ), the ratio of CO 2 produced to O 2 consumed. Consider the complete combustion of glucose :

C6H12O6 1 6 O2 ¡ 6 CO2 1 6 H2O Glucose

The RQ for glucose is 1. Now consider the oxidation of a typical fatty acid , palmitate :

C16H32O2 1 23 O2 ¡ 16 CO2 1 16 H2O Palmitate

The RQ for palmitate oxidation is 0.7. Thus, as aerobic exercise intensity increases, the RQ will rise from 0.7 (only fats are used as fuel) to 1.0 (only glucose is used as fuel). Between these values, a mixture of fuels is used (Figure 27.12).

What is the optimal mix of fuels for use during a marathon? As suggested above, this is a complex question that varies with the athlete and level of train-ing. Studies have shown that, when muscle glycogen has been depleted, the power output of the muscle falls to approximately 50% of maximum. Power output decreases despite the fact that ample supplies of fat are available, sug-gesting that fats can supply only about 50% of maximal aerobic effort. Indeed, depletion of glycogen stores during a race is referred to as “bonking” or “hit-ting the wall , ” with the result that the athlete must greatly reduce the pace.

How is an optimal mix of these fuels achieved? A low blood-sugar level leads to a high glucagon/insulin ratio, which in turn mobilizes fatty acids from adipose tissue . Fatty acids readily enter muscle, where they are degraded by b oxidation to acetyl CoA and then to CO 2 . The elevated acetyl CoA level decreases the activity of the pyruvate dehydrogenase complex to block the conversion of pyruvate into acetyl CoA. Hence, fatty acid oxidation decreases the funneling of glucose into the citric acid cycle and oxidative phosphorylation. Glucose is spared so that just enough remains available at the end of the marathon to increase the pace as the finish line draws near . The simulta-neous use of both fuels gives a higher mean velocity than would be attained if glycogen were totally consumed before the start of fatty acid oxidation. It is important to bear in mind that fuel utilization is only one of many factors that determine running ability.

If carbohydrate-rich meals are consumed after glycogen depletion, glycogen stores are rapidly restored. In addition, glycogen synthesis continues during the consumption of carbohydrate-rich meals, increasing glycogen stores far above normal. This phenomenon is called “super compen-sation” or, more commonly, carbo-loading.

81527.4 Effects of Exercise

RQ

A

B

Maximal aerobiceffort

Light aerobiceffort

100%

Carbohydrate utilization

50%

0%

100%

Fat u

tiliz

atio

n

50%

0%

1.0

0.9

0.8

0.7

FIGURE 27.12 An idealized representation of fuels use as a function of aerobic exercise intensity. (A) With increased exercise intensity, the use of fats as fuels falls as the utilization of glucose increases. (B) The respiratory quotient (RQ) measures the alteration in fuel use.

(103 mol of ATP at best) are insufficient to provide the 150 mol of ATP needed for this grueling event. Much larger quantities of ATP can be obtained by the oxidation of fatty acids derived from the breakdown of fat in adipose tissue, but the maximal rate of ATP generation is slower yet than that of glycogen oxidation and is more than 10-fold slower than that with creatine phosphate. Thus, ATP is generated much more slowly from high-capacity stores than from limited ones , accounting for the different velocities of anaerobic and aerobic events. Fats are rapidly consumed in activities such as distance running, explaining why extended aerobic exercise is beneficial for people who are insulin resistant.

Is i t possible to determine the contribution of each fuel as a function of exercise intensity? The percentage contribution of each fuel can be measured with the use of a respirometer, which measures the respiratory quotient (RQ), the ratio of CO 2 produced to O 2 consumed. Consider the complete combustion of glucose :

C6H12O6 1 6 O2 ¡ 6 CO2 1 6 H2O Glucose

The RQ for glucose is 1. Now consider the oxidation of a typical fatty acid , palmitate :

C16H32O2 1 23 O2 ¡ 16 CO2 1 16 H2O Palmitate

The RQ for palmitate oxidation is 0.7. Thus, as aerobic exercise intensity increases, the RQ will rise from 0.7 (only fats are used as fuel) to 1.0 (only glucose is used as fuel). Between these values, a mixture of fuels is used (Figure 27.12).

What is the optimal mix of fuels for use during a marathon? As suggested above, this is a complex question that varies with the athlete and level of train-ing. Studies have shown that, when muscle glycogen has been depleted, the power output of the muscle falls to approximately 50% of maximum. Power output decreases despite the fact that ample supplies of fat are available, sug-gesting that fats can supply only about 50% of maximal aerobic effort. Indeed, depletion of glycogen stores during a race is referred to as “bonking” or “hit-ting the wall , ” with the result that the athlete must greatly reduce the pace.

How is an optimal mix of these fuels achieved? A low blood-sugar level leads to a high glucagon/insulin ratio, which in turn mobilizes fatty acids from adipose tissue . Fatty acids readily enter muscle, where they are degraded by b oxidation to acetyl CoA and then to CO 2 . The elevated acetyl CoA level decreases the activity of the pyruvate dehydrogenase complex to block the conversion of pyruvate into acetyl CoA. Hence, fatty acid oxidation decreases the funneling of glucose into the citric acid cycle and oxidative phosphorylation. Glucose is spared so that just enough remains available at the end of the marathon to increase the pace as the finish line draws near . The simulta-neous use of both fuels gives a higher mean velocity than would be attained if glycogen were totally consumed before the start of fatty acid oxidation. It is important to bear in mind that fuel utilization is only one of many factors that determine running ability.

If carbohydrate-rich meals are consumed after glycogen depletion, glycogen stores are rapidly restored. In addition, glycogen synthesis continues during the consumption of carbohydrate-rich meals, increasing glycogen stores far above normal. This phenomenon is called “super compen-sation” or, more commonly, carbo-loading.

81527.4 Effects of Exercise

RQ

A

B

Maximal aerobiceffort

Light aerobiceffort

100%

Carbohydrate utilization

50%

0%

100%

Fat u

tiliz

atio

n

50%

0%

1.0

0.9

0.8

0.7

FIGURE 27.12 An idealized representation of fuels use as a function of aerobic exercise intensity. (A) With increased exercise intensity, the use of fats as fuels falls as the utilization of glucose increases. (B) The respiratory quotient (RQ) measures the alteration in fuel use.

RQ=  CO2/O2  =  1  

RQ=  CO2/O2  =  0,7  

¿QUÉ  SUSTRATO  OXIDAMOS?  

GLUCOSA  

PALMÍTICO  

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(103 mol of ATP at best) are insufficient to provide the 150 mol of ATP needed for this grueling event. Much larger quantities of ATP can be obtained by the oxidation of fatty acids derived from the breakdown of fat in adipose tissue, but the maximal rate of ATP generation is slower yet than that of glycogen oxidation and is more than 10-fold slower than that with creatine phosphate. Thus, ATP is generated much more slowly from high-capacity stores than from limited ones , accounting for the different velocities of anaerobic and aerobic events. Fats are rapidly consumed in activities such as distance running, explaining why extended aerobic exercise is beneficial for people who are insulin resistant.

Is i t possible to determine the contribution of each fuel as a function of exercise intensity? The percentage contribution of each fuel can be measured with the use of a respirometer, which measures the respiratory quotient (RQ), the ratio of CO 2 produced to O 2 consumed. Consider the complete combustion of glucose :

C6H12O6 1 6 O2 ¡ 6 CO2 1 6 H2O Glucose

The RQ for glucose is 1. Now consider the oxidation of a typical fatty acid , palmitate :

C16H32O2 1 23 O2 ¡ 16 CO2 1 16 H2O Palmitate

The RQ for palmitate oxidation is 0.7. Thus, as aerobic exercise intensity increases, the RQ will rise from 0.7 (only fats are used as fuel) to 1.0 (only glucose is used as fuel). Between these values, a mixture of fuels is used (Figure 27.12).

What is the optimal mix of fuels for use during a marathon? As suggested above, this is a complex question that varies with the athlete and level of train-ing. Studies have shown that, when muscle glycogen has been depleted, the power output of the muscle falls to approximately 50% of maximum. Power output decreases despite the fact that ample supplies of fat are available, sug-gesting that fats can supply only about 50% of maximal aerobic effort. Indeed, depletion of glycogen stores during a race is referred to as “bonking” or “hit-ting the wall , ” with the result that the athlete must greatly reduce the pace.

How is an optimal mix of these fuels achieved? A low blood-sugar level leads to a high glucagon/insulin ratio, which in turn mobilizes fatty acids from adipose tissue . Fatty acids readily enter muscle, where they are degraded by b oxidation to acetyl CoA and then to CO 2 . The elevated acetyl CoA level decreases the activity of the pyruvate dehydrogenase complex to block the conversion of pyruvate into acetyl CoA. Hence, fatty acid oxidation decreases the funneling of glucose into the citric acid cycle and oxidative phosphorylation. Glucose is spared so that just enough remains available at the end of the marathon to increase the pace as the finish line draws near . The simulta-neous use of both fuels gives a higher mean velocity than would be attained if glycogen were totally consumed before the start of fatty acid oxidation. It is important to bear in mind that fuel utilization is only one of many factors that determine running ability.

If carbohydrate-rich meals are consumed after glycogen depletion, glycogen stores are rapidly restored. In addition, glycogen synthesis continues during the consumption of carbohydrate-rich meals, increasing glycogen stores far above normal. This phenomenon is called “super compen-sation” or, more commonly, carbo-loading.

81527.4 Effects of Exercise

RQ

A

B

Maximal aerobiceffort

Light aerobiceffort

100%

Carbohydrate utilization50%

0%

100%

Fat u

tiliz

atio

n

50%

0%

1.0

0.9

0.8

0.7

FIGURE 27.12 An idealized representation of fuels use as a function of aerobic exercise intensity. (A) With increased exercise intensity, the use of fats as fuels falls as the utilization of glucose increases. (B) The respiratory quotient (RQ) measures the alteration in fuel use.

GRASAS   CARBOHIDRATOS  

Trabajo  aeróbico  liviano   Trabajo  aeróbico  intenso  

(ejempl:  25%  VO2  max)   (ejemplo:  85%  VO2  max)  

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SÍNTESIS  Y  DEGRADACION  DE  PROTEÍNAS  EN  MÚSCULO  

PROTEÍNAS  

Síntesis  

Degradación  

AMINOÁCIDOS  

ATP   ADP  

AA  

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SÍNTESIS  Y  DEGRADACION  DE  PROTEÍNAS  EN  MÚSCULO  

PROTEÍNAS  

Síntesis  

Degradación  

AMINOÁCIDOS  

INSULINA  

ATP   ADP  

AA  

+  

-­‐  

INSULINA  

Roedores  jóvenes  y  lechones    

Rumiantes  Humanos  

POSTPRANDIAL  

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SÍNTESIS  Y  DEGRADACION  DE  PROTEÍNAS  EN  MÚSCULO  

PROTEÍNAS  

Síntesis  

Degradación  

AMINOÁCIDOS  

INSULINA  

ATP   ADP  

AA  

POSTABSORPTIVO  

AYUNO  

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SÍNTESIS  Y  DEGRADACION  DE  PROTEÍNAS  EN  MÚSCULO  

PROTEÍNAS  

Síntesis  

Degradación  

AMINOÁCIDOS  

ATP   ADP  

AA  

+  

HORMONA  DE  CRECIMIENTO  

+  

LARGO  PLAZO  CRECIMIENTO