MT2

Question 1

What is an ion channel?

Answer 1

An ion channel is a transmembrane protein that allows for rapid, passive flow of one or more ions down their electrochemical gradient.

They are created through 500+ distinct ion channel subunit genes that can further form more diverse iion channels through different splicing and modification of subunits.

Question 2

How can you distinguish ion channels?

Answer 2

1. Selectivity - Type of ions passing through channel
2. Gating - Cause of the open/closing of gate (voltage, light, etc.)
3. Regulation - What agonize/antagonize the channel?
4. Conductance - How permeable the channel is to the ion per unit time?
5. Kinetics - Temporal properties of gates (is it fast [T-type] or slow closing [L-type]) and whether it closes by itself

Question 3

How can ion channels be selective?

Answer 3

Selective permeable occurs by using the physical characteristics of the channel pore, such as relative size and charge of the pore.

• Charge: Amino acid residues within the pore stripes ion of water shell 💧 and tries to stabilize molecule through non-covalent interactions.
• Size: The diameter of the pore limits the size of ions that are able to pass through the channel. (Larger = no entry)

Question 4

How can we classify channels by gating? Name and describe functions of some different gates.

Answer 4

Gating is defined by what causes the movement of the gate to open (induces the receptor to make a conformation change).

Examples:
- Leak channels: Are ungated and always open (cause of RMP)
- Voltage gated: Open and close depending on Vm in relation to the Vthreshold
- Ligand-gated: Receptor site is external or internal and is activated by chemical signals
- Mixed gating: Either requires one of or all of a selective feature to activate. (E.G.) NMDAR glutamate receptor requires both voltage and ligand gating
- Mechanical
- temperature
- light - (E.x.) channelrhodposin

Question 5

Aspects used to define a channel with conductance.

Answer 5

1. Amount of ions that pass through channel per unit time
2. Rectification - Direction of net ionic movement (Describe with inward or outward)

Question 6

Explain I-V curves and their relation to rectification.

Answer 6

I-V curves are a measure of current received in relation to the potential voltage difference in a cell (measured through membrane voltage). When there are no permeable ions within the experiment, there will be a linear I-V curve as the ions do not buffer/alter the current. However, when there is an inward rectification/flow of ions, the I-V curve will plateau as the gate will allow for the membrane voltage to be supplied by the external ions rather than from increasing current. However, if there is an exponential I-V curve, it will be an outward rectification due to positive ions exiting from the internal, causing a spike in current reading and little change of the membrane.

Question 7

What is the ion channel hypothesis? What supports this hypothesis?

Answer 7

Ion channel hypothesis: Distinct molecules formed protein channels that open and close that cause the changing in axonal membrane (Vm).

Evidence
- Pharmacological
— α-bungarotoxin antagonizes ligand-gated ion channels in skeletal muscle but not voltage-gated channels, leading to the discovery that different ions channels were mediated by multiple effector molecules. α-toxins modify kinetic propterites such as prevention of channel inactivation or activation. β-toxins lowers membrane threshold.

Question 8

What are patch clamps and their uses? Name different types of patch clamping techniques.

Answer 8

Patch clamp is a recording method that allows direct recording of individual channels through the use of specialized glass pipette electrode.