Chapter 4: Ion Channels and Transporters

What is a limitation of the voltage clamp method?

It measured the combined current from thousands of ion channels

What did the patch clamp method allow researchers to measure?

Current flowing through a single ion channel

How does the patch clamp method make contact with the membrane?

A tiny pipette forms a tight seal with a small patch of membrane

What is cell-attached recording?

a patch clap method where current from a single channel flows into the pipette

What is whole-cell recording?

A patch clamp method where the pipette interior becomes continuous with the cell cytoplasm.

What do inside-out and outside-out recordings allow researchers to study?

Effects of intracellular and extracellular molecules on ion channels

How do patch clamp currents compare with voltage clamp currents?

they are much smaller because they measure individual channels

How do individual ion channels open and close?

In a random matter

What affects the probability that an ion channel will open?

the membrane potential

What do both Na+ and K+ channels contain?

Voltage sensorsH

How do Na⁺ and K⁺ channels differ?

They differ in their activation and inactivation

What is the function of a selectivity filter?

To determine which ions can pass through an ion channel.

How many subunits form the pore of a bacterial K⁺ channel?

4 subunits

What structure forms the tunnel through a K⁺ channel?

a pore formed by channel subunits

Where is the selectivity filter located?

At the narrow opening of the channel pore.

What happens to K⁺ before it enters the selectivity filter?

it is dehydrated H

How many binding sites does K+ move through in the selectivity filter?

Four binding sites

What are the four main types of ion channels?

Voltage-gated, ligand-gated, thermosensitive, and mechanosensitive.

What activates voltage-gated ion channels?

Change in the membrane potential

What allows the voltage sensor to respond to membrane potential?

Positive charges within the sensor.

What happens to voltage sensors during depolarization?

they move outwards

What happens to voltage sensors during hyperpolarization?

They move inwards

How does the movement of the voltage sensor open and close the channel

it pulls or pushes helical linkers connected to the pore

Which ions can have voltage-gated channels?

K⁺, Na⁺, Ca²⁺, and Cl⁻.

What activates ligand-gated ion channels?

Chemical signals

Are ligand-gated channels usually highly selective?

No, they are generally less selective

What ions often pass through excitatory ligand-gated channels?

Na+ and K+

What are examples of intracellular second messengers that can affect ligand-gated channels?

Ca²⁺, cAMP, cGMP, and protons

What sensory functions can ligand-gated channels help with?

odor and light transducton

What are thermosensitive ion channels involved in?

sensation of pain and temperature

What causes thermosensitive cation channels to open?

Specific temperaturer ranges

What is an example of ligand activation of a thermosensitive channel?

Spicy foods

What activates mechanosensitive ion channels?

Mechanical distortion of the plasma membrane.

What are examples of mechanosensitive channel functions?

Muscle stretch receptors and hearing.

How can mechanical stimuli open mechanosensitive channels?

Extracellular blade structures act as levers to open the pore.

Why do nerve cells need active transporters?

To restore ion gradients disturbed during neural signaling.WHy ar

Why are they called active transporters?

They use energy to move ions against their graidents

How does active transport compare with diffusion through channels?

It is slower

What are the two main types of active transporters?

ATPase pumps and ion exchangers

Where does ATPase pump get its energy?

From ATP hydrolysis.

What is the main role of the Na⁺/K⁺ ATPase pump?

To maintain Na+ and K+ concentration graidents

How many K⁺ ions are transported into the cell by the Na⁺/K⁺ pump?

2 K+

How many Na⁺ ions are transported out of the cell by the Na⁺/K⁺ pump?

3Na+

What does ATP binding promote in the Na⁺/K⁺ pump?

Na+ binding and K+ release

What does phosphorylation promote in the Na⁺/K⁺ pump?

Na+ release and K+ binding

What does the Na⁺/K⁺ pump require to function?

ATP and K+

Do ion exchangers use ATP directly?

No

What provides the energy for ion exchangers?

Electrochemical gradients of other ions.

Which ion most commonly moves down its gradient to drive exchangers?

Na+

What is an antiporter?

An exchanger that moves ions in opposite directions

What is an example of an antiporter?

The Na⁺/Ca²⁺ exchanger.

What is the function of the Na⁺/Ca²⁺ exchanger?

To help keep intracellular Ca²⁺ low.

What is a cotransporter

a transporter that moves mulpitle ions in the same direction tip

What is an example of a cotransporter?

The Na⁺/K⁺/Cl⁻ cotransporter.

What ultimately creates the gradients that drive ion exchangers?

ATPase pumps