The Cardiac Action Potential Flashcards
Types of Potassium Channels (5)
I (k1) - Inward Rectifier
I (TO1) - Transient Outward
I (KS, KR, KUR)-Delayed Rectifier
slow, rapid, ultra-rapid
Explain I (k1) - Inward Rectifier (always open )
allows K+ diffusion mostly inward. If mV is less than -95mV (in).
If mV is greater than -95mV (out - loses functionality as membrane gets +
Phase 0 - Depolarization
1) Na+ (voltage gated) - Activate
2) Calcium (T-Type) - Activate
3) K+ (inward rectifier) - Inactivate
Phase 1 - Early Repolarization
1) Na+ (voltage gated) - Inactivate
2) K+ (transient outward)-Activate
3) Calcium (L-Type) - Activated
Phase 2 - Mid Repolarization
1) I (TO1) - Inactivate
2) Calcium (L-Type) - Activated
3) I (KS, KR, KUR) - Activated
4) Na-Ca - Activated
Why is the Na-Ca channel activated?
High intracellular Ca++ concentration activates the exchanger, pushing 3 Na+ into cell and 1 Ca++ out (more +)
Phase 3 - Repolarization, 4 - Resting Potential
1) I (K1) - Activating (see graph, 4*)
2) Calcium (L-Type) - inactivate
3) I (K**S, KR, KUR) - Activated
4) Na-Ca - inactivated
Rectifier
Transient
Rectifier - To make right
Transient - Lasting Short time
Define Inactivation & Deactivation
- Inactivation gate closes
2. Activation gate closes
At low mV activation gates are _______, inactivation gates are _______, High mV?
Think of figure:
closed, open
open , closed
Gimme Distribution of Channels
mostly same, Delayed rectifier I(kur) in atria more than ventricles,
Ca (t-type) - mostly in SA, AV nodes
How do Action potentials of the atrium and ventricle differ
More pronounced (shorter) P1 phase because of increased expression of I (kur) on the atrium
Phase 4 (SA, AV)
1) I(f - funny (PM)) - non specific ion channel - opens at low voltage
- -> Depolarization
2) I (k1) - resist depolarization
3) Ca ++ (T- Type) - open late –> D
Phase 0 (SA, AV)
1) Ca++ (T- Type) - open late –> D
2) Ca++ (L - Type) - open late –> D
*no Na++ –> slower AP - not as many Calcium channels
Phase 3 (SA, AV) II
I(k1) opens –> repolarization
What causes AV nodal Delay
CA++ channels are slower, fewer gap junctions.
Clinical Correlation - Explain MI and how it lead to scarring, how that can cause arrhythmias
– See page 49
What are the Modulatory (regulatory) channels of the heart
I (k-ach) - in SA, AV nodes; Open at REST with parasympathetic stimulation,
I (k-atp) - Preserver of ATP, opens when low ATP
Both resist depolarization, lower heart rate (hyperpolarization)
I (Cl,camp) - brings mp back to rest during plateau in toward -55mV E(Cl)
What potassium channels are stimulated by the PNS, CNS
PARA- I (k-ach) - in SA, AV nodes; Open at REST with PS stimulation, resists depolarization/contraction
I (K s, r, ur) Delayed Rectifier -
more open at re-polarization with S stimulation, Shortens AP, increased rate!!!
What causes the slow graded response in smooth muscle tissue?
- large synapses - varicosities
- Signaling molecules diffuse to signal
- B1, A, musk.. receptors are spread out.
Describe I (K1)
Inward Rectifier - Potassium channels.
Only brings K+ in at very neg. mV (which is never). between -95 to 0, it pushes potassium out of the cell making the cell inside more (negative) – Resisting Depolarization
