Lecture 9: Study of Ion Channels

What are the four main properties of ion channels?

1. ions need to move across the membrane at high rates
2. Channels need to make use of electrochemical gradient
3. Channels must be specific to specific types of ions
4. Some channels must be sensitive to voltage changes across the membrane

What does the patch clamp method allow us to do and see?

* Allows experimenters to examine ion channels one at a time
* We can see probabilities of an individual ion channel opening or closing under different circumstances (e.g. voltage changes)

Microscopic currents

Flow through individual channels

Macroscopic currents

summations of microscopic currents

Do K+ channels inactivate with brief depolarizations?

No they do not

What are the three voltage gated ion channel states?

1. Closed
2. Open
3. Inactivated

Closed voltage gated ion channel

not conducting ions but ready to be opened

open voltage gated ion channel

conducting ions

Inactivated voltage gated ion channel

closed (at a different site, typically) and not ready to be opened

Inactivation is…

what causes the refractory period which keeps action potentials from moving in two directions

Why does the action potential only spread in one direction, and not both ways, including back to the cell body?

Because voltage sensitive Na+ channels are briefly inactivated after they open

What are the advantages of the Xenopus Oocytes

* Good expression systems

– Will translate almost any RNA you inject

– You can even control the amount of protein assembled by controlling the amount of RNA you inject

– Ultimate control over ion channels you record from: mutate ion channel proteins to get different characteristics, etc

What can we learn from patch clamp studies?

* Does the ion channel inactivate right away?
* At what voltage does the channel activate (open)?

Why do Different K+ channels, even though they conduct the same ion, have different voltage response features?

because of their different molecular configurations

What are the three different response features of the K+ ion channels?

1. some never inactivate
2. some inactivate rapidly
3. some activate at hyper-polarized voltage