Ion Channels

Question 1

Individual channels during the action potential

Answer 1

• Individual currents
• summing them together makes a smooth current

Question 2

Individual channels

Answer 2

• Individual Na+ channel currents
• Summed inward Na+ current > smooth (down)
• Individual K+ channel currents
• Summed outward K+ current (up)
• Net current.

Question 3

Local anesthesia binds to voltage-gated Na+ channels and…

Answer 3

• ## prevent them from opening.

Question 4

What effect do local anesthetics have on action potentials?

Answer 4

• No rising phase (the currents are dependent on each other)

Question 5

How would the current flow across a membrane during depolarization (below) change in the presence of local anesthesia?

Answer 5

• No inward current, but delayed outward current persists
  -> still get potassium currents
  ->the currents are not dependent on each other

Question 6

The poison dart frog produces Batrachotoxin
- Batrachotoxin causes Na+ channels to…

Answer 6

• inactivate more slowly.
• Falling phase would be less steep

Question 7

K+ channels are diverse:

Answer 7

• the response of different types of K+ channels to
  depolarizing and hyperpolarizing current steps

Question 8

How can you tell if a channel is voltage-gated or not?

Answer 8

• Outward current last for a lot longer, then slope rapidly decreases
• Inactivation does not show long lasting out current and a steep hyperpolarization

Question 9

Voltage-gated channels

Answer 9

• Large variety (Na+, K+, Ca++, mixed)
• Variations between different regions of the same cell.
• Variations between cell types
  1) affects synaptic responsiveness and
  spontaneous behavior
  2) may help infer identity of cell on the basis of
  spontaneous activity.

Question 10

Neurological diseases caused by altered ion channels:

Answer 10

*Epilepsy:
- reduced Na+ channel function
- slowing of Na+ channel inactivation
- voltage-gated K+ channel mutations (reduction in K+ current)
- Ca++ channel mutations

Migraines…
- can also be caused by alterations in Voltage-gated channels

Question 11

Familial hemiplegic migraines:

Go through study in slide

Answer 11

Caused by mutations in calcium channels

Study how these mutations affect
- whole cell currents
- single channel currents