Electrophysiology

Question 1

The action potential triggers

Answer 1

Contraction

Question 2

How does the cardiac muscle AP differ from the skeletal muscle AP?

Answer 2

Duration of cardiac AP is longer

Question 3

What generates the resting membrane potential of cardiac myocytes?

Answer 3

Relative permeability to charged ions and Ion pumps

Question 4

Then, different ion concentrations create the

Answer 4

Electrical potential difference

Question 5

A change in the electrochemical gradient for an ion that is permeable can alter the

Answer 5

Resting membrane potential

Question 6

A change in ion conductance can alter the

Answer 6

Resting membrane potential

Question 7

What is the effect on RMP for a cell if there is decreased Extracellular concentration of K+?

Answer 7

RMP becomes more negative

Question 8

When we have loss of Na+/K+ ATPase due to ischemia, what happens to the RMP?

Answer 8

Becomes more negative

Question 9

Characterized as rapid depolarization

Answer 9

Cardiac myocyte AP phase 0

Question 10

In phase 0, action potential depolarizers cell to threshold (from -90 to -60), then we see rapid opening of

Answer 10

Voltage-gates Na+ channels

Question 11

Voltage-mediated activation of fast Na+ channels allows

Answer 11

Rapid depolarization

Question 12

Inactivate quickly during phase 0 so that conductance decreases

Answer 12

Voltage-gated Na+ channels

Question 13

Inactivated channels cause the

Answer 13

Refractory period

Question 14

What determines the rate of rise of the phase 0 upstroke?

Answer 14

Inward Na+ current

Question 15

What is the effect of a pharmacological blockade of Na+ channels on the cardiac myocyte AP?

Answer 15

Peak would be lower and amplitude would be lower

Question 16

How would a pharmacologic blockade of Na+ channels change the ECG?

Answer 16

QRS would be prolonged

Question 17

How would phase 0 change if we had an increase in extracellular K+?

Answer 17

Cell slowly depolarizers and RMP becomes more positive

Question 18

Slow depolarization from excess extracellular K+ causes Na+ channels to go from

Answer 18

Closed to inactive, without being activated

Question 19

What is phase 1 of the cardiac myocyte AP?

Answer 19

Brief Repolarization

Question 20

Characterized by a transient outward current (IKto) and rapid inactivation of FAST Na+ channels

Answer 20

Brief repolarization

Question 21

Cells in the subepicardium are characterized as having a

Answer 21

Shorter AP

Question 22

Phase 2 of the cardiac myocyte AP is?

Answer 22

Plateau phase

Question 23

The major current leading to the plateau phase is the

Answer 23

Slow inward Ca2+ through L-type channels

Question 24

Major Ca2+ channel in cardiac cells

-important pharmacologic targets

Answer 24

L-type channels

Question 25

Counter-balance inward Ca2+ during the plateau phase

Answer 25

Outward K+ currents

Question 26

Permits sufficient calcium entry into the cell to maintain the stores required for contraction

Answer 26

Plateau phase

Question 27

Keeps the fast sodium channels inactivated for a substantial period of time to prevent too frequent APs

Answer 27

Plateau phase

Question 28

Phase 3 of the cardiac myocyte AP is

Answer 28

Repolarization

Question 29

Results in repolarization

Answer 29

IKr current

Question 30

The action potential becomes narrower and we get faster repolarization if the

Answer 30

IKr current increases

Question 31

What changes would we see in the cardiac myocyte action potential with a drug that blocks IKr?

Answer 31

Prolonged repolarization and longer AP

Question 32

What changes would we see in the ECG of a patient taking a drug that blocks IKr?

Answer 32

Long QT interval

Question 33

A long QT interval predisposes patients for

Answer 33

Arrhythmias

Question 34

Phase 4 of the cardiac myocyte AP is the

Answer 34

Stable resting membrane potential

Question 35

Characterized by a stable RMP, a sustained period of depolarization, and a LONG duration (150-250 msec)

Answer 35

Cardiac myocyte Non-pacemaker AP

Question 36

Characterized by cells that lack the inward rectifying type of K+ channel (IK1) so RMP is less negative

Answer 36

Pacemaker potential

Question 37

Characterized by an unstable RMP, automaticity, and no sustained plateau

Answer 37

Pacemaker APs

Question 38

Phase 0 of the cardiac pacemaker potential is

Answer 38

Depolarization

Question 39

During phase 0 of pacemaker potentials, we see increase Ca2+ conductance via

Answer 39

Voltage-gated L-type Ca2+ channels

Question 40

One major characteristic of pacemaker potentials is that there is NO

Answer 40

Fast Na+ current

Question 41

Phase 3 of the cardiac pacemaker potential is

Answer 41

Repolarization

Question 42

In a pacemaker potential, depolarization leads to opening of

Answer 42

Delayed rectifier K+ channels

Question 43

Phase 3 of the pacemaker potential ends when the cell reaches the

Answer 43

Maximum negative diastolic potential

Question 44

Phase 4 of the cardiac pacemaker potential is the

Answer 44

Spontaneous depolarization cardiac pacemaker current

Question 45

Which 3 currents contribute to the cardiac pacemaker current (phase 4)?

Answer 45

IF (funny current), outward K+ (IK+), and inward Ca2+ (ICa2+)

Question 46

Activated by hyperpolarization (Anything greater than -50 mV) -The more negative the membrane potential, the more intense this current is

Answer 46

Funny current (IF)

Question 47

The “funny” current is regulated by

Answer 47

CAMP

Question 48

The IF current moves through channels called

Answer 48

HCN channels

Question 49

Is reverse-voltage dependent and has no inactivation state

Answer 49

Funny current

Question 50

The HCN channels of the funny current are permeable to

Answer 50

Na+ AND K+

Question 51

The K+ ion is more easily conducted across HCN channels, BUT under physiologic conditions, HCN channels carry

Answer 51

Inward Na+ current

Question 52

Reverse-voltage dependence makes them unique among ion channels

Answer 52

HCN channels

Question 53

Causes increased HCN activity

Answer 53

cAMP

Question 54

The opening and closing of HCN channels determines the slope of

Answer 54

Phase 4

Question 55

Activated towards the end of phase 4 of pacemaker potential

Answer 55

Inward Ca2+ (T-type) channels

Question 56

Accelerates the rate of diastolic depolarization

Answer 56

T-type channels

Question 57

Which three factors influence the intrinsic firing rate of the pacemaker cells?

Answer 57

1. ) Slope of phase 4 2. ) Maximum negative diastolic potential 3. ) Threshold potential

Question 58

The primary pacemaker is the

Answer 58

SA node

Question 59

Has the fastest rate and suppresses the firing of other pacemakers

Answer 59

SA node

Question 60

SA node activity is regulated by the

Answer 60

Autonomic Nervous System

Question 61

The regulation of heart rate is called

Answer 61

Chronotropy

Question 62

Increasing sympathetic ton causes an increase in

Answer 62

HR (positive chronotropic effect)

Question 63

Increasing vagal tone causes a

Answer 63

Decrease in HR

Question 64

In the heart, norepinephrine binds to

Answer 64

B1 adrenergic receptors

Question 65

When norepinephrine binds to B1 adrenergic receptors, we see an increase in

Answer 65

cAMP

Question 66

This increase in cAMP has what two main effects?

Answer 66

1. ) Stabilized HCN in open position | 2. ) Opens L(and likely T)-type Ca2+ channels

Question 67

When acetylcholine is release, what does it bind to in the heart?

Answer 67

Muscarinic receptors (M2)

Question 68

When acetylcholine binds muscarinic receptors (M2), it decreases

Answer 68

cAMP and If

Question 69

Acetylcholine binding M2 activates a LIGAND-gated

Answer 69

K+ channel

Question 70

Activation of the ACh-gated Ik will

Answer 70

Hyperpolarize the cell