Session 4-Electrical And Molecular Mechanisms In CVS

Question 1

True or false: Na+ permeability sets the RMP

Answer 1

FALSE - K+ permeability

Question 2

What is the intracellular K+ concentration?

Answer 2

~140mM

Question 3

What is the extracellular K+ concentration?

Answer 3

~4mM

Question 4

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

Answer 4

OUT

Question 5

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

Answer 5

TRUE

Question 6

Why is RMP not exactly equal to Ek at rest?

Answer 6

Very small permeability to other ion species eg. Na+

Question 7

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

Answer 7

Cardiac myocytes

Question 8

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

Answer 8

FALSE - increase

Question 9

Why is a rise in calcium required?

Answer 9

To allow actin and myosin interaction (contraction)

Question 10

What is phase 0 of the ventricular AP?

Answer 10

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

Question 11

What happens in phase 1 of the ventricular AP?

Answer 11

Transient outward K+ current - initial fast repolarisation

Question 12

What happens in phase 2 of the ventricular AP?

Answer 12

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

Question 13

What happens in phase 3 of ventricular AP?

Answer 13

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

Question 14

How much longer is diastole than systole?

Answer 14

2/3

Question 15

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

Answer 15

TRUE

Question 16

Complete the sentence:

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

Answer 16

Myocyte

Spontaneously

Question 17

Which channels make up the funny current?

Answer 17

HCN channels

Question 18

What are HCN channels activated by?

Answer 18

Hyperpolarisation

Question 19

Which ions are HCN channels permeable to?

Answer 19

Na+

K+

Question 20

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

Answer 20

Funny current

Question 21

When is the pacemaker potential activated?

Answer 21

At membrane potentials more negative than -50mV

Question 22

What does ‘HCN’ channels stand for?

Answer 22

Hyperpolarisation-activated Cyclic Nucleotide-gated channels

Question 23

What causes the upstroke of the SA node AP?

Answer 23

Opening of voltage-gated Ca2+ channels

Question 24

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

Answer 24

Opening of voltage-gated K+ channels

Question 25

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

Answer 25

TRUE

Question 26

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

Answer 26

Bradycardia

Question 27

What can occur if AP fail in the heart?

Answer 27

Asystole

Question 28

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

Answer 28

Tachycardia

Question 29

What happens if electrical activity becomes random in the heart?

Answer 29

Fibrillation

Question 30

What is the normal plasma K+ concentration range?

Answer 30

3.5-5.5mmol/L-1

Question 31

What plasma K+ concentration constitutes as hyperkalaemia?

Answer 31

>5.5 mmol/L-1

Question 32

What plasma concentration constitutes as hypokalaemia?

Answer 32

<3.5 mmol/L-1

Question 33

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

Answer 33

K+ permeability dominates resting membrane potential

Question 34

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.

Answer 34

Depolarises Slows down Less Na+

Question 35

What is the risk of hyperkalaemia?

Answer 35

Heart can stop-asystole

Question 36

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

Answer 36

TRUE

Question 37

What are the possible treatments for hyperkalaemia? (2)

Answer 37

1) Calcium gluconate-makes heart less excitable | 2) Insulin and glucose-insulin promotes K+ moving into cell

Question 38

What is the effect of hypokalaemia?

Answer 38

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

Question 39

What is the problem with hypokalaemia?

Answer 39

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)

Question 40

What can ventricular fibrillation lead to?

Answer 40

No cardiac output

Question 41

What does depolarisation open in the T-tubule system?

Answer 41

L-type Ca2+ channels

Question 42

What does localised Ca2+ entry open in the SR?

Answer 42

Calcium-induced calcium release channels (CICR)

Question 43

What % of Ca2+ enters across sarcolemma?

Answer 43

25%

Question 44

What % of Ca2+ is released from SR?

Answer 44

75%

Question 45

What is the tone of blood vessels controlled by?

Answer 45

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

Question 46

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

Answer 46

Myosin light chain

Question 47

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

Answer 47

Must be phosphorylated

Question 48

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

Answer 48

Calmodulin Myosin light chain kinase Phosphorylates

Question 49

What dephosphorylates the myosin light chain?

Answer 49

Myosin light chain phosphatase

Question 50

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

Answer 50

PKA

Question 51

What initiates the contraction of vascular smooth muscle cells?

Answer 51

Depolarisation or activation of alpha-adrenoceptors