Cardiac APs

Question 1

Significance of IK1 Channels:

Answer 1

• These create the INWARD rectifier current.
  • Does not “gate” like other channels:
• passes + charge more easily into the cell than out of the cell.
  • Functions to maintain resting membrane potential by making minor changes in potential
  ○ Either influx or efflux of potassium

Question 2

Significance of If currents:

Answer 2

• HCN tetramer
• Funny current: Considered “funny” because it is turned off at depolarized potentials and on at hyperpolarized potentials
○ Ability to be activated at hyperpolarization is important in pacemaker cells w/o neuronal stimulus b/c it allows AP firing without stimulus from innervation
• Permeable to both Na and K

Question 3

“Overdrive suppression”

Answer 3

other cells have pacemaker activity and can become pacemakers, but that SA nodal firing suppresses this activity. Other sites are:
• Can be located in:
1. AV node and purkinje fibers
2. Ectopic pacemaker cells:

Question 4

Why is the SA node the dominant pacemaker activity?

Answer 4

it has the highest intrinsic rate of automaticity

Question 5

Ectopic pacemaker cells:

Answer 5

Can be cells that display automaticity (like SA node) because of hypoxic conditions

Question 6

During the refractory periods, there is still inactivation of what current?

Answer 6

INa
It is not until there is complete removal of inactivation of INa and deactivation of IKr and IKs, that a normal action potential can be initiated.