3A. The figure on the left depicts a cell-attached patch clamp experiment which
ID: 202394 • Letter: 3
Question
3A. The figure on the left depicts a cell-attached patch clamp experiment which is recording the changes in current through a single voltage-gated Na' channel (VGSC) when the membrane was first clamped to a hyperpolarized potential and “-40 80 -then clamped to a depolarized potential for 15msec. The current recordings were 15 0 10 Time (ms) repeated during seven individual trials. Closed In your answer, address the following: (1) What do the current recordings say about the probability of VGSC opening at depolarized membrane potentials? (2) What observations can be made regarding the “open time" of VGSCs while the membrane is depolarized? (3) How does the structure of the VGSC protein influence the pattern and shape of VGSC activation? Be sure to address why the channel seems to open and close once (if at all) even though the membrane remains depolarized. Use the space provided below (5 pts): -'uwu enr. 0 5 10 15 Time (ms) aueaguuawExplanation / Answer
When the VGSC opens up, sodium ions start moving into the membrane. This is known as depolarization. Sodium channel are closed once the membrane is depolarized so that no more lowering of membrane voltage occurs.
So, the recordings tell us that VGSC will remain closed at the depolarized membrane potential (-80mV as according to the figure).
2)
The membrane remains open for 15ms as according to the given diagram.
3)
The shape of the VGSC channel is altered by the membrane potential. In the resting state, the channel is closed. When an electric potential triggers the membrane, then, sodium channel open up causing sodium ions to rush into the membrane.
The voltage gated channel has 6 subunits with a central pore. The six subunits are actually 6 membrane spanning alpha helices. These are named as S1 to S6. Out of the 6 subunits, the S4 subunit senses the voltage.
In resting state, the subunits move over the central pore so that it remains closed. When the membrane potential changes due to an electric impulse, then the central pore is pushed apart due to repulsive forces. This causes a conformational change in the sodium channel, and makes it open up.
A second conformational change causes the channel to close in the depolarized membrane.
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