Lecture 4

Ion selectivity

A property of ion channels that are selectively permeable to some ions and not to others.

Voltage-gated ion channels are always open.

FALSE

True or false: Potassium ion channels are never voltage-gated.

False

Microscopic currents

Flow through individual channels

Name some similarities and some differences between macroscopic currents and their underlying microscopic currents.

Macroscopic are made up of microscopic currents They are typically in the same direction

How are the patch-clamp and voltage-clamp techniques the same? How are they different?

Same- involve ion currents, involve the membrane Different- voltage-clamp involves adding electrical potential, patch-clamp involves PINCHING the cell membrane, patch-clamp looks at ion channels ONE at a time

Macroscopic currents

Summations of microscopic currents

True or false: Voltage-gated ion channels are specific to individual ion species.

TRUE

Voltage-gated channel: inactivated state

closed / not ready

Voltage-gated channel: open state

conducting

Patch-clamp method

experimenters can examine ion channels one at a time

Stretch-activated ion channels

ion channels that open in response to some mechanical signal

Ligand-gated ion channels

normally closed, open when ligand binds to channel

Voltage-gated channel: closed state-

not conducting, ready

Voltage sensor

senses the voltage of the membrane (if high enough it'll open)