C-Electrical Activity of the Heart

Question 1

Heart rate controlled by pacemaker cells in the SA node. SA nodal cells fire intrinsically at ___________. Rate modulated by ANS.

Answer 1

~100/min.

Parasympathetic tone slows rate to 60-80/min.

Question 2

These cells are normally driven by action potentials originating in the SA node (overdrive suppression).

Answer 2

atrioventricular node (AV node)

Question 3

ectopic pacemakers

Answer 3

Abnormal circumstances–> AV node (or others, especially in damaged myocardium) can take over initiation of the heartbeat,

Question 4

Cell-to-cell propagation of the action potential from the SA node to other regions occurs via _______

Answer 4

gap junctions

Question 5

The _______________, is the only place where action potentials can propagate from the SA node to the ventricles

Answer 5

atrioventricular node (AV node)

Question 6

From the AV node, additional conducting pathways propagate the action potential to the left and right ___________

Answer 6

ventricles

Question 7

Cardiac Action Potentials vary between regions and are categorized as ___________

Answer 7

“fast” or “slow”

arise from different regions of the heart

Question 8

a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory.

Answer 8

Action potential

Question 9

Nernst Potential, Eion
ENa—> +58
ECa—> +124
EK—> ______

Answer 9

-90

Question 10

Current flowing into cell causes depolarization

Current flowing out of cell causes ______

Answer 10

hyperpolarization

Question 11

Direction of current flow depends on __________ (Vm) and ion gradient (Nernst Potential, Eion)

Answer 11

membrane potential

Question 12

Nernst Potential, Eion
ENa—> _____
ECa—> +124
EK—> -90

Answer 12

+58

Question 13

Current flowing into cell causes _______

Current flowing out of cell causes hyperpolarization

Answer 13

depolarization

Question 14

Direction of current flow depends on membrane potential (Vm) and _______

Answer 14

ion gradient (Nernst Potential, Eion)

Question 15

Cardiac sodium channels- Ion gate is _______ at rest/hyperpolarized

Answer 15

Closed

Question 16

Inactivation vs deactivation ion gate

Answer 16

deactivation- activation gate is closed (activation gate)

inactivation- Inactivation gate is plugging channel

different processes

Question 17

The properties of calcium channels are mainly determined by the________

Answer 17

principle (CaV) subunit

L type- high volt
T type- low volt

Question 18

Ca Channel-Calcium currents:
High Voltage Activated (HVA)
Both voltage- and calcium-dependent inactivation

Answer 18

ICa-L, L-type current

Question 19

Ca Channel-Calcium currents:
Low-Voltage Activated (LVA)
Voltage-dependent Inactivation

Answer 19

ICa-T, T-type current

Question 20

IKs (KvLQT1 tetramer + minK) mutations can cause

Answer 20

long QT

Question 21

IK1 (Kir tetramer) functions to

Answer 21

lowers rate of pacemaker

Question 22

______ is an “anti-target” tested in preclinical evaluation of new drugs

Answer 22

HERG

HERG produces IKr
Reducing IKr can result in arrhythmias

Question 23

Because _____ (tetramer of HERG) is important for repolarization of both fast and slow cardiac action potentials, altered HERG function can disrupt normal cardiac electrical activity, leading to arrhythmias.

Answer 23

IKr

Question 24

HERG channels are blocked by a wide variety of_______

Answer 24

structurally unrelated compounds

Question 25

You _____ want to block HERG

Answer 25

DO NOT

all drugs must be tested with HERG to avoid arrhythmias