Reactive Oxygen Species

Question 1

What are reactive oxygen species?

Answer 1

Highly reactive metabolites of molecular oxygen

Question 2

How are reactive oxygen species produced?

Answer 2

Primarily a by-product of the incomplete reduction of oxygen in the respiratory chain

Question 3

How are reactive oxygen species produced?

Answer 3

They are a by-product of the incomplete reduction of oxygen in the respiratory chain

Question 4

Examples of reactive oxygen species

Answer 4

Superoxide anion
Hydrogen peroxide
Hydroxyl radical
Peroxinitrite

Question 5

What are NADPH oxidases?

Answer 5

Major source of ROS in the cell

Question 6

NADPH oxidases contain how many enzymes?

Answer 6

They are multimeric enzymes

Question 7

True or false:
There is only one isoform of the NOX catalytic subunit

Answer 7

False - there are many (Nox1-5, Duox1/2)

Question 8

Is NOX2 active or inactive?

Answer 8

It exists in both active and inactive states

Question 9

What ROS does NOX2 produce?

Answer 9

Superoxide

Question 10

Is NOX4 active or inactive?

Answer 10

Constituently active

Question 11

What ROS does NOX4 produce?

Answer 11

Hydrogen peroxide

Question 12

NOX2 and NOX4 produce high/low levels of ROS

Answer 12

Low

Question 13

What roles does NOX2 play in CVD?

Answer 13

Atherosclerotic lesion formation
Determining size of infarct after ischaemic reperfusion injury
Calcium release from SR

Question 14

What does NOX4 protect the vasculature against?

Answer 14

Inflammatory stress

Question 15

How are ROS generated from NOX2?

Answer 15

Physiological stretch activates activates NOX2 generating ROS

Question 16

Where does ROS production take place?

Answer 16

Sarcolemmal and T-tubule membranes

Question 17

True or false:
ROS production triggers the release of calcium sparks?

Answer 17

True, they are mediated via RyR in the SR

Question 18

Stretch increases/decreases the frequency of sparks?

Answer 18

Increases

Question 19

Is the activity of the RyR redox sensitive?

Answer 19

Yes

Question 20

How is the LTCC inhibited?

Answer 20

By oxidation as it is redox sensitive

Question 21

Free radicals inhibit/potentiate LTCC?

Answer 21

Inhibit

Question 22

What is the effect of chemical oxidation of sodium channels?

Answer 22

It impairs their rapid inactivation, meaning there is a longer depolarising current, a longer action potential and this can lead to arrhythmogenesis and sodium overload

Question 23

Effect of oxidants such as H2O2 on SERCA and the NCX

Answer 23

Inhibit SERCA
Activate NCX

Question 24

How does H2O2 reduce the size of the calcium transient?

Answer 24

H2O2 enhances removal of calcium from cells and reduces calcium re-uptake into SR
Calcium content of SR becomes more and more empty, leading to the reduction in size of the calcium transient

Question 25

What is glutathionylation?

Answer 25

Post-translational modification in which glutathione reversibly binds to thiol groups on proteins via disulphide bonds

Question 26

What is glutathione?

Answer 26

A cellular reducing agent

Question 27

Which subunit of the Na pump undergoes glutathionylation under oxidative stress to reduce its activity

Answer 27

The beta subunit

Question 28

ROS are positively/negatively inotropic?

Answer 28

Negatively inotropic, depress cardiac contractility

Question 29

How does ROS reduce the size of the calcium current?

Answer 29

By activating the RyR, depleting the SR of Ca Inhibits the LTCC

Question 30

How does ROS prolong the AP?

Answer 30

Slows the inactivation of LTCC

Question 31

Which type of PKA is redox active?

Answer 31

Type I PKA

Question 32

How is PKA I activated?

Answer 32

Activated by hydrogen peroxide which promotes the formation of disulphide bond between 2 regulatory subunits

Question 33

Voltage gated calcium channels: What are they phosphorylated by? What is the effect of the phosphorylation?

Answer 33

Phosphorylated of Rad by PKA Increases trigger calcium and increases CACR

Question 34

RyR: What are they phosphorylated by? What is the effect of the phosphorylation?

Answer 34

Phosphorylated by PKA Increases calcium release from SR

Question 35

SERCA2a/PLB: What is it phosphorylated by? What is the effect of the phosphorylation?

Answer 35

PLB phosphorylated by PKA Increases SERCA activity, increasing Ca reuptake into SR, increasing Ca store and gives rise to bigger calcium transients

Question 36

Sodium pump: What is it phosphorylated by? What is the effect of the phosphorylation?

Answer 36

PLM phosphorylated by PKA Increases Na efflux, preventing Na overload

Question 37

Troponin I: What is it phosphorylated by? What is the effect of the phosphorylation?

Answer 37

TnI phosphorylated by PKA Reduced affinity of TnC for Ca, reduction in contraction of cardiac muscle and accelerates relaxation

Question 38

Biochemical changes ischaemia

Answer 38

Switch to anaerobic ATP production Metabolite accumulation

Question 39

Which metabolites accumulate in ischaemia?

Answer 39

Protons (cause acidosis) Phosphate Free radicals Potassium Oxidised lipids

Question 40

What happens in the baroreceptor reflex?

Answer 40

Increased sympathetic stimulation Increased contractility Increased oxygen demand

Question 41

How does impaired pumping accelerate glycolysis?

Answer 41

Briefly increases glucose uptake into myocyte Inhibits glycogen synthetase Activates phosphofructokinase reaction

Question 42

Why does glycolysis fail under ischaemic conditions?

Answer 42

Lack of substrate to metabolise Lack of oxidised NAD Metabolic acidosis

Question 43

Consequences of metabolic acidosis in ischaemica

Answer 43

Inhibition of NCX and RyR (this is protective) Reduces action potential velocity Protons compete with Ca for binding to specific sites on proteins

Question 44

Acidosis occurs quickly/slowly after the onset of ischaemia

Answer 44

Very quickly

Question 45

Acidosis occurs quickly/slowly after the onset of ischaemia

Answer 45

It occurs extremely rapidly

Question 46

What is the primary explanation for impaired heart contractility in ischaemia?

Answer 46

Acidosis reduces calcium affinity, maximum tension and contractility of myofilaments

Question 47

Function of NCX

Answer 47

Regulates intracellular pH through exchange of intracellular H+ for extracellular Na

Question 48

What is HNE?

Answer 48

A major lipid peroxidation product formed during oxidative stress

Question 49

What does HNE do?

Answer 49

Reacts with thiol groups on proteins altering their activities

Question 50

What is the garden hose effect?

Answer 50

Perfusion of the intracoronary vessels has a distending effect on the cardiac muscle, distension of the cardiac muscle is positively inotropic

Question 51

How does impaired relaxation arise in early and late ischaemia?

Answer 51

Early - inhibition of Ca efflux Late - formation of rigor bonds

Question 52

Changes to the cardiac action potential in ischaemia

Answer 52

Delayed activation Slower to rise (due to less Na channels in resting state) Slower to trigger Ca channels Reaches threshold more slowly AP propagates more slowly

Question 53

What causes cells to die in ischaemia?

Answer 53

Calcium activated proteases degrade proteins and long chain AcylCoA disrupts sarcolemma

Question 54

What is reperfusion injury?

Answer 54

Restoration of blood flow following ischaemia results in a substantial increase in number of cardiomocytes that die

Question 55

What causes reperfusion injury?

Answer 55

Abnormal calcium handling Oxidative stress Mitochondrial dysfunction

Question 56

Mitochondrial Permeability Transition Pore (mPTP) opening is acclelerated/decelerated by Ca and Ros

Answer 56

Accelerated

Question 57

Myocytes appear to be ___ years younger than the person they're from?

Answer 57

10 years younger