Pacemaker Activity/Repetitive Firing

Question 1

SK Channels

Answer 1

Slow K+ channels that require only Ca to open, prolonged hyperpol and prevent firing and thus a burst of APs

Question 2

BK Channels

Answer 2

High conductance big K+ channels that require Ca and depol to open, so they close upon repol

Question 3

3 Special Channels in Heart Muscle

Answer 3

T Type Ca Channel - activated near threshold in late diastole
L Type Ca Channel - activated to maintain plateau
Kv7 - slow rectifier, re/hyperpolarizes

Question 4

2 Effects of NE on Heart Potential

Answer 4

Elevates plateau and shortens duration

Question 5

Ih (HCN Channels)

Answer 5

Hyperpolarization activated nonspecific cation channel that always tries to bring potential to -20, heart cell can’t ever take a break

Question 6

NE Molecular Effect

Answer 6

Increases cAMP, which binds to channels and makes them easier/faster to open, especially shifting Ih to the right making it open at less neg membrane potential so you get faster heart rate

Question 7

ACh Molecular Effect

Answer 7

Betagamma subs from Gi from MR bind and activate Kir channel, slowing HR

Question 8

Kir

Answer 8

Hyperpolarizationa activated K channel that turns off (blocked by Mg) as threshold reached and K driving force increases

Question 9

TrpC Channels

Answer 9

Activated by Ca and ACh to give depolarizing pacemaker current in entorhinal cells. Blocked by flufenamic acid and PLC inhibitors

Question 10

Entorhinal Cortical Cell Feedback Cycle

Answer 10

AP -> L type Ca -> fast Kv channels repol -> Ca activates TrpC channels if ACh primed -> depol to threshold again