Cardiac Ion Channels and Action Potentials Flashcards Preview

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Flashcards in Cardiac Ion Channels and Action Potentials Deck (18)
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1

Which cells have fast cardiac action potential

myocardial cells and cells of rapid conduction pathways

bundle of His, left and right bundle branches and Purkinje fibers

2

Which cells have slow cardiac action potential

pacemaker cells of SA and AV nodes

3

Fast Action Potential
Phase 0 = initial upstroke

Na+ in

INa = rapidly activated by depolarization

4

Fast Action Potential
Phase 1 = partial repolarization

little K+ out

IKto = transient K+ current both activated and inactivated by depol at a slower rate than Na+ current

5

Fast Action Potential
Phase 2 = prolonged plateau

Ca2+ in balanced by K+ out

ICa-L =activated by depol and inactivated by voltage and calcium dependent inactivation

IKr and IKs = rapid and slow delayed rectifiers
activated by depol

6

Fast Action Potential
Phase 3 = rapid repol

K+ out

Inactivatate ICa-L and incr activation of IKr and IKs

7

Fast Action Potential
Phase 4 = resting potential

Permeable to K+

IK1 = inward rectifier suited for holding cells at Ek (Nernst potential) by quickly correcting changes in potential through efflux or influx of K+

8

Slow Action Potential
Phase 0 = upstroke phase

ICa-T and ICa-L = L-type and T-type calcium channels = slow action potential (NO INa)

L-type = High voltage Activated
T-type = low voltage activated

9

Slow Action Potential
Phase 3 = repolarization

Balance between ICa, IKr/IKs

10

Slow Action Potential
Phase 4 = pacemaker potential

If = funny current induced by hyperpolarization
permeable to Na+ and K+

deactivate IKr/IKs
activate ICa-T

11

Do pacemaker cells require neuronal input?

No but they fire slow APs

Never reach stable resting potnetial--> continuosuly and repetitively fire slow APs

12

Difference between Fast and Slow Action Potentials
CHANNELS

Fast = INa and Ik1
Slow = If (activ at hyperpolarization) and ICa-T (activ at low voltage)

13

Function of IK1

No Gating

maintain cell at resting Ek by correcting changes in potential via influx/efflux of K+ (NO OUTWARD CURRENT ON DEPOLARIZATION)

14

Function of If

Turned on ONLY AT HYPERPOLARIZED

impt for automaticity in nodal cells

15

What is mechanism of overdrive suppression?

SA node controls electrical activity of other, less active and less frequent pacemakers in the heart (AV node...)

16

What is absolute refractory period?

NO STIMULUS CAN EVOKE ACTION POTENTIAL after fast AP

because still inactivation of INa

17

What is relative refractory period?

STRONGER THAN NORMAL STIMULUS REQUIRED

18

When can you fire another action potential?

when you have inactivation of INa and deactivation of IKr and IKs before normal stimulus