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분야
hwpExperiments (1-1) : Potassium Channels
A) The proability that the channel is open increases in a sigmoid manner with time. Explain why?
Experiments (1-2) : Sodium Channelshbn
A) When the channel closes, which gate is usually the culprit? Does the inactivation ("h") gate ever reopens once it closes?
B) Try-10mV, and compare the behavior of gates and the channel.
Program (2) : Conductances
Experiments (2-1) :for voltage dependence of Na and K conductance
A) How do the Na and K conductances change?
B) Why doesn't the Na conductance ever reach the maximum? Note again that Na channels inactivate and K channels do not.
program (3) : currents
Experiment (3-1) :
From a fixed holding potential (e.g -60mV), step to a variety of test potentials (between -40 and +100mV). Compare the Na and K conductance that you studied earlier.
Experiment (3-2): Reversal potential of Na channel
A) Find the reversal potential for the Na current; that is the membrane voltage where there is no current because there is no driving force, since the membrane potential=the Na equilibrium potential. Note that the Na currents reverse direction there ( hence the name).
Experimets (3-3) : Reversal potential of K channel
A) Find the reversal potential for the K currents.
Program (5) : Action potential
Experiments (5-1): Generation of action potential
Experiments (5-2): Refractory period
A) Does a second action potential form?
B) How does its shape and size compare to that of the first action potential?
C) What happens? Can you explain the change in action potential shape and in Na conductance?
D) Would you expect these action potentials to be actively propagated?
E) When was the axon in its absolute refractory period? When was it in its relative refractory?
Program (6) : Expanded Scales
Experiments (6-1): Threshold and Accommodation
A) Try to find the minimum stimulus amplitude that gives an action potential. Threshold is defined as depolarized voltage where the cell will generate an action potential.
B) Try an intial membrane potential of -55mV. How do the threshold voltage and the minimum stimulus change? Explain the reason for the threshold change.
Program (7) : Pharmacology
Experiments (7-1): Sodium channel blocker (STX)
Sketch the results and explain the effect of STX on the shape of the action potential.
Experiments (7-2): Potassium channel blocker (TEA)
Repeat the experiment by increasing TEA “dosages” from 0.5, 1, 5, 10mM.
Sketch and explain the results.
Experiments (7-3): Spontaneous firing
Look at what happened with 1mM TEA on the slow (50ms) scale. Do any cells do things like this normally? Sketch and explain the results.
Program (8) : Ion Substitution
Experimets (8-1) : Effect of higher or lower than normal K+ in ECF
A) What happens to the resting potential? What happens to the action potential? Sketch the results.
B) See what happens at longer times (50ms scale) when you increased external K concentration.
Experimets (8-2) : Effect of lower than normal Na+ concentration In ECF
Now try lowering Na(Large increase in Na are not phusiological, as that would make the
external sodium hypertonic).
Experiments (1-1) : Potassium Channels
A) The proability that the channel is open increases in a sigmoid manner with time. Explain why?
Potassium(K+) channel의 경우 Sodium channel(Na+)과 달리 inactivation gate가 없고 activation gate만 4개를 가지고 있으며, 이를 n gate라고 한다. 막전압의 변화는 세포막에 존재하는 전하를 띤 물질의 구조적 변화를 일으켜 n gate를 열리게 한다. K+ channel은 저분극시 random으로 열리고 닫히며, 파란색 그래프에서 볼 수 있듯 4개의 gate가 모두 열렸을 경우에만 K+ channel의 conductance가 증가하여 channel이 열리고 ion의 이동이 시작된다. 만약 gate가 1개의 gate의 구조적 변화에 의해 열린다면 막전압 변화에 의한 K-전도도의 증가는 단순 지수함수적으로 일어날 것이다. 하지만 실험을 통해 실제 위와 같이 4가지의 n gate가 모두 열린 경우에만, 즉 세포막에 존재하는 4개의 gate가 모두 구조적 변화를 일으켜야만 열리는 것을 알 수 있다.
따라서 본 문제에서 command potential 값이 0mv 인 경우로 Depolarization(저분극) 시켰을 때 4개의 gate가 동시에 열릴 확률은 n의 4제곱형태인 n4에 비례하는 모양의 그래프가 나타나며, 이것이 sigmoid, 즉 S자 형태를 띠게 된다. 이를 수학적으로 표현하면 n gate 한 개에 대해서 channel이 열릴 확률은 으로 계산되므로, 4개의 gate 에 대해서는 해서는 의 확률을 따르게 되며, 이 그래프의 모양은 Sigmoid, 즉 S자 형태가 된다.
Stuart Ira Fox, 박인국(역) (2004). 생리학 (7판). 라이프사이언스. 105~112.
