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Anoxia Tolerance > General > Flashcards

General Flashcards

1
Q

How much does [GABA] increase to during anoxia?

A

[GABA] increases from 3 to 27 uM.

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2
Q

What is one biological advantage of Oxygen reduction (used in ATP generation)?

A

Oxygen reduction provides among the largest free energy per electron transfer.

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3
Q

Why would fossorial animals need to be hypoxia tolerant?

A

Fossorial animals are those that burrow underground where Oxygen partial pressures are low.

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4
Q

(Andrews, 2004)

A

Mitochondrial ATP production decreases nearly tenfold.

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5
Q

What kinases restrict entry of glycolytic intermediates into the tricarboxylic acid cycle.

A

Pyruvate dehydrogenase kinases (Pdk) restrict entry of intermediates (Sugden, 2006).

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6
Q

What are the Phd enzymes?

A

HIF prolyl hydroxylases that regulate the stability of HIF. May be oxygen sensitive (Bruick 2001).

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7
Q

(Bruick, 2001) and (Epstein, 2001)

A

Described HIF prolyl hydroxylases (PHD1-3).

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8
Q

Name one key regulator of Pdk4.

A

Ppar-alpha upregulates Pdk4. Restricts entry of glycolytic intermediates into TCA (Argones, 2008).

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9
Q

What effect does inhibiting Phd1 have?

A

1) Increases hypoxia tolerance.
2) Decreases efficency of oxidative metabolism through Ppar-alpha.
3) Increases oxygen conservation.
4) Prevents oxidative damage.

(Argones, 2008)

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10
Q

What effect does knocking out Phd1 have on oxygen consumption?

A

Decreases oxygen consumption in mice myofibers. (Argones, 2008)

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11
Q

(Argones, 2008)

A

Knocking out Phd1 increases hypoxia tolerance, reduces Oxygen consumption.

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12
Q

How can you measure mitochondrial respiration rate through complex I?

A

High-resolution respirometry and supplementing pyruvate + malate and excess ADP.

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13
Q

How can you measure mitochondrial respiration rate through complex II?

A

High-resolution respirometry and supplementing succinate and excess ADP.

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14
Q

What effect does knocking out Phd1 have on mitochondrial glucose respiration?

A

Decreased respiration through complex I but no changes in complex II.

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15
Q

What effect does Phd1 deficiency have on fatty acid oxidation?

A

No effect. Instead it reduces pyruvate entry into TCA cycle.

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16
Q

Which enzyme converts pyruvate into acetyl CoA?

A

Pyruvate dehydrogenase complex (PDC) (Harris, 2000).

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17
Q

What is EPR oximetry?

A

Electron paramagnetic resonance oximetry. Can be used to measure oxygen delivery (Argones, 2008).

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18
Q

What happens to the PCr pool during hypoxia in wild-type mice and Phd1-deficient mice?

A

PCr is rapidly used to regenerate ATP. However [Pi] still increases, suggesting ATP use is greater than ATP regeneration. In Phd1-deficient mice, PCr actually increased over time after an initial increase during the first 30 min of ischemia.

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19
Q

What does increased [Pi] tell us about ATP usage in the cell?

A

ATP is being used up faster than it is made.

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20
Q

What roles do Phd2-3 play in hypoxia tolerance?

A

None as far as we know (Argones, 2008)

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21
Q

What is the rate of ATP generation in turtle brain?

A

About 18.4 umol per 100 mg of tissue every hour (Robin, 1979).

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22
Q

How is the fraction of ATP derived from glycolysis different in turtles than mammals?

A

A greater fraction of ATP is derived from glycolysis in turtles. Turtles have no Pasteur Effect as a result. Already operating at peak glycolytic rate (Robin, 1979).

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23
Q

How well do Oxygen electrodes function below 10 torr?

A

Not well, Clark electrodes are notorious for having problems below 10 torr (Robin, 1979).

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24
Q

What is the expected ratio of oxygen consumed per molecule of glucose during aerobic respiration?

A

6 mol of oxygen is consumed per mol of ATP (Lehinger, 1971)

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25
Q

What is the expected amount of ATP generation for every molecule of lactate consumed?

A

1 mol of ATP is generated per mole of lactate (Lehinger, 1971)

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26
Q

How does the rate of lactate production during normoxia compare with the rate during anoxia in the turtle brain?

A

They are not significantly different. Normoxic lactate production is high in the turtle brain (much higher than rat) because turtle already operates at peak glycolytic capacity. (Robins, 1979)

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27
Q

How does ATP generation in rat brain compare with turtle brain? What does this say about each brain’s energy requirements?

A

ATP generation in rat and turtle brain are similar (19 vs 18.4 umol ATP/100 mg/hr). Shows that ATP requirements in rat and turtle brain are similar. (Robins, 1979)

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28
Q

Which tissues have the highest PyKi activity? What advantage does this provide?

A

Skeletal muscle has the highest PyKi activity, subserves the energy requirements of burst activity during exercise. Allows high rates of glycolysis. (Robins, 1979)

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29
Q

What is the ratio of brain-to-skeletal muscle PyKi activity in turtles? What does this say about glycolytic rate in turtle brain?

A

Suggests PyKi activity in brain is high which means high glycolytic rate. Also suggests that in turtle brain activity of rate-limiting-glycolytic enzymes is high.

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30
Q

(Shaw, 1935)

A

Early description of turtle anoxia tolerance.

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31
Q

(Jackson, 1974)

A

Arterial Oxygen pressure drops to zero after first hour of diving. Despite extrapulmonary modes of respiration.

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32
Q

What does cyanide do to mitochondrial ATP generation?

A

Mimics anoxia by inhibiting cytochrome aa3 and abolishing mitochondrial ATP generation (Robin, 1964)

33
Q

(Belkin, 1968)

A

Brain death occurs prior to heart death under hypoxia.

34
Q

Why is the brain a good model for quantitative bioenergetic analysis?

A

Substrate limited to glucose (Siesjo, 1978). Makes it easy to measure substrate use.

35
Q

Does the turtle have a reserve of high energy phosphate intermediates (ATP, PCr)?

A

No because inhibiting glycolysis with monoiodoacetate caused brain death during anoxia. Suggests glycolysis using glucose from liver reserves is still important.

36
Q

Monoiodoacetate

A

A glycolytic inhibitor which can also cause osteoarthritis.

37
Q

To what end product does glycolysis proceed to in oyster and bivalves?

A

Stops at phosphenolpyruvate, PyKi activity is lacking. Alanine, propionate, succiante and an unknown compound from pyruvate and alanine accumulate instead of lactate (Saz, 1971).

38
Q

What alternate pathways does the turtle have other than glycolysis?

A

None, all lactate production was accounted for by glucose consumption (Robins, 1979) (Buck, 2000).

39
Q

How high is the activity (not content) of superoxide dismutase in turtle brain?

A

Superoxide dismutase appears to vary inversly with oxidate state of cell (Simon, 1977). Turtle has low activities of superoxide dismutase.

40
Q

Is enhanced glycolytic rate enough to survive anoxia?

A

No because glycolysis still only provides at most about 25% of basal energy requirements (Robin, 1979). Must deal with lactic acidosis which progressively decreases glycolytic rate, and reduce basal energy requirements.

41
Q

How is turtle PFK different from mammal PFK?

A

Turtle phosphofructokinase is insensitive to inhibitory control from ATP. Instead PCr inhibits PFK. (Storey 1974)

42
Q

What doe the right-to-left shunt in reptiles do?

A

The R-L shunt allows mixing of oxygenated and deoxygenated blood. Can allow for better thermoregulation when diving.

43
Q

When did oxygen form, and what was its origin?

A

Oxygen is thought to have had a biological origin (cyanobacteria) and formed approximately 2 billion years ago.

44
Q

What are some extrapulmonary surfaces for respiration in the turtle?

A

The well-vascularized epithelium lining the throat and cloaca exchange gases (Ultsch, 1985).

45
Q

What is a significant element of freeze tolerance?

A

A significant element of freeze tolerance is ischemia/anoxia tolerance, since freezing freezes blood flow and oxygen delivery to organs. However species of freeze tolerant hatchlings vary in their ability to survive anoxia (Dinkelacker 2005).

46
Q

Why might adult turtles be more tolerant than hatchling turtles?

A

Adult turtles may have larger glycogen stores, and more extrapulmonary surfaces for respiration. Additionally hatchling turtles with underdeveloped shells may not be able to buffer lactate as well as adult turtles (Reese, 2004).

47
Q

What is the turtle’s first response to decreasing oxygen?

A

Before severe hypoxia, the turtle increases ventilation, cardiac output and hemoglobin affinity. (Lutz, 1997) (Jackson, 2002).

48
Q

What are lactate concentrations in the turtle after several winter months?

A

Lactate concentrations reach as high as 150-200 mM (Ultsch, 1987) (Jackson, 2000 and 2007). Exceeds turtle’s bicarbonate buffering capacity of 34-45 mM. In comparison humans have lactate of 20-25 mM (Jackson 2011).

49
Q

What are some issues with relying too much on glycolysis?

A

Quick depletion of carbohydrate fuel reserves and accumulation of acidic end products (Kelly, 1988) (Jackson, 2002).

50
Q

(Hochachka, 1996)

A

Turtle hepatocytes show a 94% decrease in overall ATP turnover during anoxia.

51
Q

What are the five main ATP consuming processes down-regulated by turtle tissue during anoxia?

A

1) Ion motive ATPases
2) Protein synthesis
3) Protein degradation
4) Gluconeogenesis
5) Urea synthesis

52
Q

What are the main features of hypometabolism as outlined by Hochahka and colleagues in 1997?

A

1) Oxygen sensing and signal transduction pathways to communicate the transition
2) A set of genes are down-regulated
3) A set of genes are up-regulated
4) Decreased activity in non-essential pathways
5) Decline membrane permeability and neuronal excitability
6) A balance of ATP use and production

53
Q

(Ackerman and White, 1979)

A

Long term strategy to conserve ATP supply is initiated once arterial Oxygen tension falls below 20 torr. Once blood PO2 fell below 20 torr, turtles reduced ventilation rate, didn’t come to surface to breath anymore.

54
Q

What are some of the damaging effects of ROS?

A

1) Peroxidation of polyunsaturated fatty acids in organelles
2) Oxidation of sulfhydryl-containing enzymes
3) Oxidation of carbohydrates resulting in polysaccharide depolymerization
4) Oxidation of nucleic acids resulting in single and double scissions

55
Q

What evidence is there of regulation of voltage-gated Na+ channel density during anoxia in turtles?

A

In turtle cerebellum, voltage-gated Na+ channel density decreases 42% during anoxia (Storey, 1990).

56
Q

(Nilsson, 1991)

A

GABA-A receptor density increases during anoxia. GABA concentrations increase 80-fold higher than normoxia.

57
Q

Name three mitogen activated protein kinase (MAPK) families.

A

Extracellular regulated kinases (ERK), c-Jun N-terminal kinase (JNK) and p38. Neither ERK or p38 seem to play a role during anoxia. JNK activates 5 hours after anoxia. In rats p38 can help with preconditioning.

58
Q

How does glycolytic rate change in turtles undergoing anoxia?

A

Glycolytic rate initially increases during the first hour then decreases after five hours of submergence.

59
Q

During normoxia, how much Oxygen is is converted into ROS in mammalian mitochondria?

A

About 1-4% turns to ROS in mammalian mitochondria due to a leaky electron transport chain (Hermes-Lima, 2001).

60
Q

Why is ROS dangerous to mitochondrion?

A

Can damage mitochondrial lipids and DNA. Triggers mitochondrial apoptosis signals.

61
Q

(Hermes-Lima, 2001)

A

Electron carriers of electron transport chain become reduced during oxygen deprivation. (Build of up reducing equivalents?). Sudden reintroduction of oxygen brings about an immediate oxidation of these carriers and over production of ROS. Turtles tolerate this stress by having high levels of antioxidant defenses much higher than other ectotherms and comparable to mammalian endotherms.

62
Q

Name two reactions that produce the dangerous hydroxyl radical from hydrogen peroxide.

A

The Fenton Reaction produces hydroxyl radicals from hydrogen peroxide by reducing iron. The Haber-Weiss reaction produces hydroxyl radicals from hydrogen peroxide and superoxide by oxidizing iron.

63
Q

What is GSH/GSSG ratio an indicator of and what changes does it show in the anoxic turtle during reoxygenation?

A

Glutathione to Glutathione disulfide ratio is an inverse indicator of oxidative stress (More GSSG than GSH when under oxidative stress). In turtles GSH/GSSG actually increases, suggesting that reoxygenation isn’t stressful. Furthermore lipid peroxidation was unaffected during recovery. SOD and GR activity does increase 45 and 64%, 24 hours into recovery however. An enzyme involved in glutathione metabolism increased 1.8 fold.

64
Q

What is protein debt and to what degree does it manifest in turtles?

A

Protein debt refers to the compensatory increase in protein synthesis that occurs after prolonged suppression of protein synthesis. In turtles this does not occur, and protein synthesis is comparable to normoxia during reoxygenation. Suggests during anoxia, there is no protein degradation either (Bailey, 1997).

65
Q

Which heat shock protein shows increased expression in anoxic turtles?

A

Hsp60 expression tends to increase, in contrast to other Hsp’s which are constitutively expressed. Hsp60 is predominantly a mitochondrial chaperone.

66
Q

(Jackson, 2004)

A

Looked at avenues for extrapulmonary oxygen respiration in western painted turtles using a sealed water container and oxygen electrode. Blocked of different openings for extrapulmonary gas exchange using acrylic cement, latex bags or surgical tape. Assumed that all extrapulmonary surfaces respire equally.

67
Q

Does dissolved oxygen concentration have any effect on overwintering survival underwater?

A

Yes since overwintering survival can depend on extrapulmonary extract of Oxygen (Reese, 2003).

68
Q

Why is extrapulmonary respiration important with regards to lactic acidosis?

A

The incoming oxygen can minimize or even avoid the problem of lactic acidosis (Jackson, 2004).

69
Q

Is there indirect evidence for dissolved oxygen content having any effect on a turtle’s respiratory state?

A

When dissolved oxygen content is high, turtles stay submerged longer before surfacing to breath (Bagatto and Henry, 1990) (Gordos and Franklin, 2002).

70
Q

Which two extrapulmonary surfaces require water pumping?

A

The mucosa of the buccopharynx (Gage, 1886; Wang, 1989) and cloaca and cloaca bursae (Gordos, 2002).

71
Q

(Crocker, 2000)

A

Found evidence that the turtle exploits aquatic Oxygen uptake when dissolved Oxygen is available at low temperature.

72
Q

What does blood pH decrease to during anoxia?

A

It decreases from 8 to about 7.6.

73
Q

Is the cloaca or buccopharynx a significant source of oxygen exchange during diving in C. picta?

A

No, not even muscle paralysis to stop cloacal pumping had any significant effect (Jackson, 2004). Buccal pumping specifically may be used for smelling instead and cloacal pumping for ion uptake and buoyancy control.

74
Q

Does skin have a major role in gas exchange in C. picta?

A

Yes blocking skin reduced oxygen uptake by 50% from 0.12 umol/g/h to about 0.06 umol/g/h. When covered in cement, they would stretch out their limbs to maximize extrapulmonary exchange similar to the behaviour seen in G. geographica in well-aerated water (Crocker, 2000).

75
Q

Name six challenges organisms must deal with during anoxia.

A

1) Fuel - Large liver glycogen stores.
2) Deal with acidosis - Shell lactate and bicarbonate stores.
3) Maximize ATP yield - marine molluscks use anaerobic pathways instead of lactate to increase ATP yield (succinate, propionate and acetate).
4) Metabolic rate depression - reduce metabolic rate by inactivating cellular processes.
5) Antioxidant defenses - to deal with reperfusion injury
6) Activate anoxia responsive genes - HIF1a and HIF2 downstream of Phd1 inactivation.

(Storey, website)

76
Q

(Ultsch, 1982) Part III.

A

Showed that hypoxia results in lactic acidosis in turtles.

77
Q

What is pulse oximetry? What are its limitations?

A

Measure hemoglobin saturation using absorbency of two wavelengths of light. Can’t measure blood PO2.

78
Q

How does Radiometer’s Blood Gas Analyzer measure different blood properties?

A

It uses an electrode for each property, including a Clark electrode for measuring oxygen.

Anoxia Tolerance (6 decks)

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