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Semester 2-CVS > Session 4-Electrical And Molecular Mechanisms In CVS > Flashcards

Session 4-Electrical And Molecular Mechanisms In CVS Flashcards

1
Q

True or false: Na+ permeability sets the RMP

A

FALSE - K+ permeability

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2
Q

What is the intracellular K+ concentration?

A

~140mM

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3
Q

What is the extracellular K+ concentration?

A

~4mM

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4
Q

Do K+ ions move into or out of the cell?

A

OUT

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5
Q

True or false: at equilibrium potential, concentration gradient and electrical gradients are equal

A

TRUE

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6
Q

Why is RMP not exactly equal to Ek at rest?

A

Very small permeability to other ion species eg. Na+

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7
Q

Which cells in the heart are electrically active and fire AP?

A

Cardiac myocytes

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8
Q

True or false: AP triggers a decrease in cytosolic [Ca2+]

A

FALSE - increase

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9
Q

Why is a rise in calcium required?

A

To allow actin and myosin interaction (contraction)

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10
Q

What is phase 0 of the ventricular AP?

A

Opening of v-gated Na+ channels, causing an upstroke. These channels open on depolarisation and then inactivate

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11
Q

What happens in phase 1 of the ventricular AP?

A

Transient outward K+ current - initial fast repolarisation

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12
Q

What happens in phase 2 of the ventricular AP?

A

Plateau phase-opening of v-gated Ca2+ channels (some K+ channels also open)

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13
Q

What happens in phase 3 of ventricular AP?

A

Repolarisation-Ca2+ channels inactivate and v-gated K+ channels open

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14
Q

How much longer is diastole than systole?

A

2/3

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15
Q

True or false: cardiac myocytes have lots of different types of K+ channels

A

TRUE

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16
Q

Complete the sentence:

The SA node is a specialised __________ with not much contractile machinery but they are ________________ active.

A

Myocyte

Spontaneously

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17
Q

Which channels make up the funny current?

A

HCN channels

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18
Q

What are HCN channels activated by?

A

Hyperpolarisation

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19
Q

Which ions are HCN channels permeable to?

A

Na+

K+

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20
Q

What contributes to the initial slope to threshold in the pacemaker potential?

A

Funny current

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21
Q

When is the pacemaker potential activated?

A

At membrane potentials more negative than -50mV

22
Q

What does ‘HCN’ channels stand for?

A

Hyperpolarisation-activated Cyclic Nucleotide-gated channels

23
Q

What causes the upstroke of the SA node AP?

A

Opening of voltage-gated Ca2+ channels

24
Q

What causes the downstroke (repolarisation) of SA node AP?

A

Opening of voltage-gated K+ channels

25
Q

True or false: SA node is fastest to depolarise so it sets the rhythm

A

TRUE

26
Q

What can occur if AP are fired to slowly in the heart?

A

Bradycardia

27
Q

What can occur if AP fail in the heart?

A

Asystole

28
Q

What can occur if AP fire too quickly in the heart?

A

Tachycardia

29
Q

What happens if electrical activity becomes random in the heart?

A

Fibrillation

30
Q

What is the normal plasma K+ concentration range?

A

3.5-5.5mmol/L-1

31
Q

What plasma K+ concentration constitutes as hyperkalaemia?

A

> 5.5 mmol/L-1

32
Q

What plasma concentration constitutes as hypokalaemia?

A

<3.5 mmol/L-1

33
Q

Why are cardiac myocytes so sensitive to changes in [K+]?

A

K+ permeability dominates resting membrane potential

34
Q

Complete the sentences:

Hyperkalaemia ______________ the myocytes and __________ _______ the upstroke of the action potential. If plasma K+ is raised then Ek gets ______ negative so membrane potential depolarises a bit and this inactivates some of the voltage-gated ___ channels.

A

Depolarises
Slows down
Less
Na+

35
Q

What is the risk of hyperkalaemia?

A

Heart can stop-asystole

36
Q

True or false: in hyperkalaemia you may initially get an increase in excitability

A

TRUE

37
Q

What are the possible treatments for hyperkalaemia? (2)

A

1) Calcium gluconate-makes heart less excitable

2) Insulin and glucose-insulin promotes K+ moving into cell

38
Q

What is the effect of hypokalaemia?

A

Lengthens action potential and delays repolarisation because when K+ lowered too much, there is an allosteric effect and the conductance of K+ channels is reduced

39
Q

What is the problem with hypokalaemia?

A

Longer action potential can lead to early after depolarisations (EADs), which can lead to oscillations in membrane potential. This can result in ventricular fibrillation (VF)

40
Q

What can ventricular fibrillation lead to?

A

No cardiac output

41
Q

What does depolarisation open in the T-tubule system?

A

L-type Ca2+ channels

42
Q

What does localised Ca2+ entry open in the SR?

A

Calcium-induced calcium release channels (CICR)

43
Q

What % of Ca2+ enters across sarcolemma?

A

25%

44
Q

What % of Ca2+ is released from SR?

A

75%

45
Q

What is the tone of blood vessels controlled by?

A

Contraction and relaxation of vascular smooth muscle cells in tunica media of arteries, arterioles and veins

46
Q

In smooth muscle cells, the activation of what allows the interaction with actin?

A

Myosin light chain

47
Q

What must happen to the myosin light chain to enable actin-myosin interaction?

A

Must be phosphorylated

48
Q

Complete the sentences:

Ca2+ binds to _________ which activates ________ _________ _______ __________ (MLCK). MLCK __________________ myosin light chain to permit interaction with actin.

A

Calmodulin
Myosin light chain kinase
Phosphorylates

49
Q

What dephosphorylates the myosin light chain?

A

Myosin light chain phosphatase

50
Q

What can phosphorylate myosin light chain kinase (MLCK) to inhibit its action?

A

PKA

51
Q

What initiates the contraction of vascular smooth muscle cells?

A

Depolarisation or activation of alpha-adrenoceptors

Semester 2-CVS (18 decks)

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