Cardiac Electrophysiology - Myocardial Cells

Question 1

what controls resting potential in fast response cardiac cells?

Answer 1

high conductance through unique K channel

Question 2

why is fast response K channel unique?

Answer 2

it closes when cell depolarizes

Question 3

what causes upstroke of AP in fast response?

Answer 3

fast Na channels

Question 4

what causes plateau of AP in fast response?

Answer 4

Ca channels

Question 5

how does repolarization occur in fast response cells?

Answer 5

Ca channels inactivate, and slow K channel opens

Question 6

when does slow K channel open?

Answer 6

doesnt open until cell has been depolarized for a long time

Question 7

what cells do fast response cardiac aP?

Answer 7

1. atrial myocytes
2. ventricular myocytes
3. purkinje conducting fibers

Question 8

what cells do slow response cardiac AP ?

Answer 8

1. SA node

2. AV node

Question 9

which AP has a plateau?

Answer 9

atria/ventricle

Question 10

how do cardiac cells prevent tetanic contraction?

Answer 10

duration of ventricular muscle AP and its effective refractory period is about as long as mechanical event (so unlikely to get another AP)

Question 11

what types of K channels exist in cardiac resting potential

Answer 11

1. voltage gated (slower or faster , longer or shorter)
2. channels regulated by NT or hormones
3. channels sensitive to intracellular metabolism like ATP

Question 12

which K channel causes efflux of K through a voltage gated channel to hyperpolarize the cell?

Answer 12

iK1 (inwardly rectifying K current)

Question 13

what controls fast upstroke of depolarization?

Answer 13

Na influx

Question 14

what controls rapid partial repolarization spike?

Answer 14

Na channels closing

Question 15

what controls plateau phase?

Answer 15

Ca influx

Question 16

what controls repolarization phase

Answer 16

Ca channels close, iK channel opens, then iTO channels, then iK1

Question 17

what controls membrane resting potential

Answer 17

iK1

Question 18

when do iK1 channels open?

Answer 18

when cell is repolarizing, not when cells are depolarized

Question 19

when does phase 0 end?

Answer 19

Na conductance drops because h gate closes (inactivation)

Question 20

what causes phase 0

Answer 20

opening of fast Na channels

Question 21

what causes phase 1

Answer 21

closing of Na channels, and transient K current iTO

Question 22

what causes phase 2?

Answer 22

sustained Ca current through voltage gated channels

Question 23

describe K conductance during phase 2

Answer 23

conductance drops because iK1 channels are closed, but some K current

Question 24

what terminates plateau?

Answer 24

delayed iK channels opening

Question 25

what is effect of sympathetic innervation on cardiac

Answer 25

B1 receptor effects via cAMP increase, increases Ca, increases force

Question 26

PSNS effect on cardiac muscle

Answer 26

muscarinic receptor via cAMP decrease, decreases Ca, decrease force

Question 27

what helps control active force in cardia cells?

Answer 27

calcium influx that controls Ca release from SR (inotropic state)

Question 28

what occurs if Ca is modified in cardiac cell?

Answer 28

modifies SR release of Ca, which changes AP and force

Question 29

what causes phase 3 repolarization?

Answer 29

Ca channels closing, iK delayed rectifying K channels opening to increase K current, then iTO opens K and Cl briefly, and then iK1 comes back.

Question 30

what is the "voltage clamp"

Answer 30

iK1 channels hyperpolarizing the cell

Question 31

what channel dominates resting membrane potential?

Answer 31

iK1