W7L2

Question 1

Passive membrane model

Answer 1

Electrical model of the membrane is a resistance and a capacitance IN PARALLEL
- membrane acts as a capacitor
- the channel acts as resistance

When inject positive current into cell or cytosol, the inside of the cell will become less negative.
- membrane depolarization is slow to rise
- once steady state is reached, there are no more voltage changes, which means the capacitance fully discharged. Then, all the current will go through the channels

Im = IC + IR

Question 2

4 configurations of patch recordings

Answer 2

You DO NOT KNOW the resting membrane potential
- when you do 1 of the 4 recordings, you put different voltages without knowledge of the resting membrane potential
- eventually, you will need to subtract the membrane potential to know exactly how much voltage you applied

All the 4 configurations are recorded in a RECORDING CHAMBER, which is filled with solutions - mimicking the extracellular or intracellular content of the cell
- this solution can be changed, which is relatively easier than changing the pipette solution

Only Whole Cell Recording allows for both voltage and current clamp.
- the other 3 configurations only allow for voltage clamp

Question 3

V-clamp: Inward current vs outward current

Answer 3

V-Clamp:

a. Inward Current I_Na+ depolarizes cell membrane
- inward current is defined as negative current

b. Outward Current I_K+ hyperpolarizes cell membrane
- outward current is defined as positive current

Question 4

I-clamp(passive membrane properties): Inward current vs outward current

Answer 4

Positive current depolarizes the membrane

Output voltage is slower than input current,
slow to rise and slow to fall

Question 5

Current-voltage relationship

Answer 5

I = GV
Ix = Gx (Em-EX)

Current on y-axis; voltage on x-axis

slope = Gx

Question 6

Voltage Clamp: K+ current alone

Answer 6

I_K = delayed rectifier current

No inactivation

The I-V curve is not linear

If you stop the voltage clamp at 4 ms (shown by dotted line in ppt), it takes some time (dotted diagonal slope) for the current to decrease.
- thus, after it is activated, it takes some time for the current to return to the resting level aka closed state
- this process is called DEACTIVATION (going from open state channel to closed state), which is different from inactivation

Question 7

Conductance changes during an AP

Answer 7

Fast Na+ conductance

Delayed K+ conductance
- due to phenomenon of deactivation (Once it is activated, it takes some time for the current to return to resting level; it doesn’t close straight away - it takes some time)