Lec 6 Cardiac Cellular Electrophysiology

Question 1

Difference in phase 0 between SA and ventricular AP?

Answer 1

Much faster in ventricle [300 V/s vs 20 V/s]

Question 2

Difference in phase 1 between SA and ventricular AP?

Answer 2

absent in SA AP

Question 3

Difference in phase 2 between SA and ventricular AP?

Answer 3

abbreviated in SA

Question 4

Difference in phase 3 between SA and ventricular AP?

Answer 4

comparable

Question 5

Difference in phase 4 between SA and ventricular AP?

Answer 5

• flatter, more negative in ventricle

- increasing [not flat] in SA

Question 6

Sequence of cardiac electrical activation [6 things]

Answer 6

1. SA node
2. Atrium
3. AV node
4. bundle of His/bundle branches
5. purkinje fibers
6. ventricles

Question 7

What AP is similar to SA node AP?

Answer 7

AV node AP

Question 8

What AP is similar to ventricular AP?

Answer 8

purkinje

Question 9

What AP is similar to atria AP?

Answer 9

none

Question 10

How does conduction speed change in different regions [where is it noticeabley slow/fast]?

Answer 10

• slow through AV node

- fast through his/purkinje

Question 11

How does voltage change in depolarization?

Answer 11

Goes from -85 mV up to 0

Question 12

How does voltage change in repolarization?

Answer 12

Goes down back to -85 mV

Question 13

What does phase 0 represent in ventricular AP?

Answer 13

Na coming in

Question 14

What does phase 1 represent in ventricular AP? [lease important to remember]

Answer 14

• Na coming in and K out [K dominates]

- short burst of repolarization

Question 15

What does phase 2 represent in ventricular AP?

Answer 15

• Ca coming in and K out

- balance out but K winning slightly so flat [gradual repolarization]

Question 16

What does phase 3 represent in ventricular AP?

Answer 16

• K+ out

- strong repolarization

Question 17

What does phase 4 represent in ventricular AP?

Answer 17

• K out dominates, a little NCX in

Question 18

Do SA node cells need stimulus to get AP?

Answer 18

NO!

Question 19

Do ventricular cells need stimulus to get AP?

Answer 19

Yes

Question 20

What is absolute refractory period [ARP]?

Answer 20

Period during action potential when its impossible to trigger a second AP

Question 21

What is relative refractory period [RRP]?

Answer 21

Period just after action potential when you need stronger stimulus to get a weak AP

Question 22

What does phase 0 represent in SA AP?

Answer 22

Ca influx [strong depolarization]

Question 23

What does phase 2 represent in SA AP?

Answer 23

Ca in and K out [K very much dominates]

Question 24

What does phase 3 represent in SA AP?

Answer 24

K out

Question 25

What does phase 4 represent in SA AP?

Answer 25

NCX and I[f] in

Question 26

What is definition of negative current?

Answer 26

positive charge flowing inward

Question 27

What type of current is positive charge flowing out?

Answer 27

positive current

Question 28

What is driving force?

Answer 28

V-Ex where V is voltage and Ex is the equilibrium voltage for that ion

Question 29

What happens to ion if V=Ex? What type of current?

Answer 29

Ion does not move in or out of cell? No current!

Question 30

What happens to ion if [V-Ex] > 0? What type of current?

Answer 30

- Ion moves out of cell | - positive current

Question 31

What happens to ion if [V-Ex] < 0? What type of current?

Answer 31

- ion moves into cell | - negative current

Question 32

At what voltages is K current positive?

Answer 32

Above -90 mV

Question 33

At what voltages is Na current positive?

Answer 33

above +70 mV

Question 34

At what voltages is Na current positive?

Answer 34

above +130 mV

Question 35

At what voltages is Na current negative?

Answer 35

below + 70 mV

Question 36

At what voltages is Ca current negative?

Answer 36

below +130 mV

Question 37

At what voltages is K current negative?

Answer 37

below -90 mV

Question 38

At what voltages does Na channel open?

Answer 38

at voltage > -60 mV

Question 39

How does Na current stop? Why?

Answer 39

- Na channel automatically closes after opening | - Opens then get current and approaches nernst equilibrium so have less driving force so current stops

Question 40

How fast does Na channel open and close?

Answer 40

4 ms

Question 41

How does Ap initiation feedback in I[NA]

Answer 41

- as you increase V [with V still below -40 mV] you get more Ina - with more current you get more positive V which provides more feedback - inward Na current depolarizes the membrane

Question 42

At what voltage does L-type Ca channels open?

Answer 42

-40 mV

Question 43

Does Na or L-type Ca open at a higher [less negative] voltage?

Answer 43

L-type Ca [thats why Na opens first]

Question 44

How long does it take for L-type Ca channel to open and close?

Answer 44

50 ms

Question 45

Does Na or L-type Ca channel open/close faster?

Answer 45

Na 10x faster

Question 46

2 mains differences Na and Ltype Ca current?

Answer 46

1. Ca opens at higher [more positive] voltage | 2. Ca opens and inactivates slower

Question 47

What role do L-type Ca channels play in ventricular myocytes?

Answer 47

- action potential plateau [phase 2] | - initiate SR Ca release

Question 48

What role do L-type Ca channels play in vSA and AV nodal myocytes?

Answer 48

- action potential upstroke [phase 0]

Question 49

What role do L-type Ca channels play in vascular smooth muscle?

Answer 49

- supply Ca for constraction

Question 50

2 types of drugs that are Ca channel blockers

Answer 50

- type IV anti-arrhythmics | - antihypertensives

Question 51

Inwardly-rectifying K channels [Ik1] - at what voltages are they open?

Answer 51

- open at -90 mV | - closes during action potential plateau [at higher voltages]

Question 52

What is function of Ik1 in ventricular myocytes?

Answer 52

- stabilizes resting potential in ventricular myocytes | - keeps voltage at -85 mV

Question 53

Delayed rectifying K channels - at what voltages are they open? function in ventricular myocytes?

Answer 53

- closed at resting potential - open with delay during plateau of AP - two type: rapid [Ikr] and slow [Iks] - repolarize membrane at end of AP plateau

Question 54

How do three K types act in ventricular AP?

Answer 54

- at begining of AP: Ik1 shuts off to allow plateau | - later: Ikr and Iks open and repolarize membrane

Question 55

Why does SA node have slow depolarization rather than flat phase 4 [2 channels involved]?

Answer 55

- inward current through NCX [3 NA in, 1 Ca out] | - inward current through "funny current"

Question 56

What is funny current I[f] in SA node?

Answer 56

- mix of Na and K but mostly Na - inward current in negative voltages, it is a depolarizing force - closed at positive voltages [during depolarization]

Question 57

What 3 things does funny current oppose

Answer 57

- normal Na current - normal Ca current - delayed rectifier K current

Question 58

Are Na channels present in SA and AV nodes? Where else are they present [2 places]

Answer 58

- No not present in SA/AV | - present in: ventricles, purkinje

Question 59

What 2 channels explain why SA nodes get spontaneous APs [automaticity] and ventricular do not?

Answer 59

- funny current present in SA not ventricle [open at negative potentials - Inward rectifier [Ik1] present in ventricle not SA [if it were present in SA would prevent spontaneous depolarization since maintains resting potential]

Question 60

How does phase 0 differ in ventricular and SA?

Answer 60

- Na and Ca in ventricle - only Ca [no Na] in Sa - Na more abundant and open faster so get much faster depolarization in ventricle compared to SA

Question 61

How does phase 3 differ in ventricle and SA?

Answer 61

Its comparable | both have lots of delayed rectifier K channels

Question 62

How does phase 4 differ in ventricle and SA?

Answer 62

- ventricle has Ik1 so stays at -85 mV so flat | - presence I[f] and absence I[k1] in SA so get slow depolarization