Electrical Properties of the Heart

Question 1

SA node Frequency of depolarization most depends on which ion?

Answer 1

Ca++

Question 2

Sympathetic and Parasympathetic Activation most changes which phase of SA action potential

Answer 2

Phase 4

Question 3

Atrial Muscle Contracts from

Answer 3

Right to Left

Question 4

Atrial Muscle action potential is most dependent upon

Answer 4

Na+

Question 5

Role of AV node

Answer 5

slow down action potential to allow ventricular filling

Question 6

List in order the rates of conduction velocity of the 4 major regions of the heart

Answer 6

Purkinje Fibrers > Bundle His > SA > AV

Question 7

Purkinje Fibers have very rapid conduction due to

Answer 7

High density of Na+ Channels

Question 8

What is the primary current and ion channel found in phase 1 of ventricular depolarization?

Answer 8

K+ via the I_to current

Question 9

What is the major ion and channel(s) found in phase 2 of ventricular depolarization

Answer 9

Ca++ via I_Ca and Na-Ca exchanger

also note outward flow of K via I Kur

Question 10

What is the major current and ion responsible for phase 3 of ventricular depolarization?

Answer 10

I_K and K

Question 11

What phase of ventricular depolarization is associated with long QT syndrome?

Answer 11

Phase 3 due to dysfunction of I_kr or I_ks, prolongs repolarization

Question 12

Characteristics of voltage gated K channel

Answer 12

6 TMD
S4 is voltage sensor
S5-S6 is P-loop that demonstrates selectivity

Question 13

Characteristics of Na and Ca voltage gated channels

Answer 13

4 Continuous 6 TMD
S4 is the voltage sensor
The pore between the 4 units is the selectivity filter

Question 14

non voltage gated K channel

Answer 14

2 TMD

P loop between M1 and M2

Question 15

HCN channels (I_f Channel)

Answer 15

6 TMD
S4 voltage gate
Pore is selectivity filter
Contains cAMP domain

Question 16

Effect of Sympathetics on Cardiac Ion channel?

Answer 16

NE act on Beta adrenergic receptors
Activates PKA increase activity of I Ca-L and I_ks
Increases cAMP levels = increase I_f activity
Greater Amplitude, Longer Plateau, Faster Repolarization

Question 17

Parasympathetic effect of cardiac ion channels?

Answer 17

Ach acts on Muscarinic receptors
Activates I_kAch channels
Activates muscarinic receptors to downregulate cAMP
modulates I_f, I_Ca-L
I_kAch maximizes diastolic action potentials

Question 18

What would be the effect of sympathetic activation without I_ks activation and only I_Ca activation?

Answer 18

Without I_ks, plateau phase would be extra long because I_ks would not be able to repolarize the cell.
NB: under normal conditions, Epi activates both I_ks and I_Ca

Question 19

What percent of families with LQTs have not yet been linked to any known genes?

Answer 19

40% => Many more genes to be identified