Cardiac Ion Channels & Action Potentials Flashcards Preview

CVPR: CV Unit I > Cardiac Ion Channels & Action Potentials > Flashcards

Flashcards in Cardiac Ion Channels & Action Potentials Deck (11)
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1
Q

Fact cardiac action potentials cell types

A

occur in myocardial cells and cells of rapid conduction pathways

2
Q

Slow cardiac action potentials cell types

A

occur in pacemaker cells of SA and AV nodes

3
Q

Channels involved in fast cardac action potentials (5)

A
  1. INa = voltage-gated sodium channel
  2. ICa-L = L-type calcium channel; activate in response to to depolarization and undergo VDI (voltage-depend. inactiv.) and CDI (calc.-depend. inact.)
  3. IKto = Potassium channel; activates/inactivates slower than Na channels upon depolarization
  4. IKr + IKs = “delayed rectifiers”; activated by depolarization
  5. Ik1 = “inward rectifier current”; holds cells near Ek between action potentials
4
Q

Channels involved in slow cardiac action potential

A
  1. ICa-T + ICa-L = ICa-T is T-type channel (LVA=low voltage activated); ICa-L is L-type channel (HVA).
  2. If = “funny” current; induced at hyperpolarization, permeable to Na+ and K+
  3. IKr + IKs = “delayed rectifiers”; activated by depolarization
5
Q

Ionic mechanisms behind spontaneous firing of pacemaker cells

A
  • balance between ICa and delayed rectifier current (IKr and IKs) –> repolarization occurs shortly after the peak of the action potential.
  • repolarization is followed by a slow depolarization (the pacemaker potential) which brings the cell back to threshold for the generation of another action potential.
  • Funny current (If): induced by hyperpolarization. Induction of If allows cation fluxes which drive voltage potential towards the reversal potential of If (-30 mV).
6
Q

Role of IK1 in fast action potentials

A
  • IK1=inward rectifier potassium channel.
  • IK1 has a strong, “instantaneous” rectification: readily conduct inward K+ current at potentials below EK and only weakly pass outward K+ current at potentials slightly positive to EK
  • responsible for HOLDING CELLS NEAR EK BETWEEN ACTION POTENTIALS without producing an outward current.
7
Q

Role of If(Ih) in slow action potentials

A
  • If generates the “funny” current—a current induced by hyperpolarization.
  • Induction of If in the context of the “slow” cardiac action potential allows cation fluxes which drive voltage towards the reversal potential of If and may play a role in generation of the pacemaker potential—which is critical to allowing pacemaker cells generate rhythmic firing in the absence of neuronal input.
8
Q

Absolute refractory period definition

A

period of time following a “fast” cardiac action potential a second action potential cannot be initiated until most of the inactivation of INa is removed (during the repolarizing phase).

9
Q

Relative refractory period definition

A

period of time following a “fast” cardiac action potential during which the threshold for a second action potential remains elevated until after repolarization is complete (complete removal and inactivation of INa and deactivation of IKr and IKs has occurred).

10
Q

Mechanism of overdrive suppression

A
  • while other myocardial cells in the heart (including AV node), are capable of spontaneous activity, they fire at a lower frequency than those of the SA node
  • usually, these cells are driven by action potentials originating in the SA node:
  • an action potential will spread to them from the SA node before they reach threshold on their own.
11
Q

Ectopic pacemakers definition

A

abnormal circumstance under which another cell besides those of the SA node take over initiation of contraction/heartbeat