Term
| What are the two voltages used in voltage clamp experiments? |
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Definition
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Term
| If membrane potential < command potential, VCA passes ______ current |
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Definition
| + current (depolarizing it) |
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Term
| If membrane potential > command potential, VCA passes ______ current |
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Definition
| - current (hyperpolarizing it) |
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Term
| What is the goal of VCA function? |
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Definition
| to make membrane potential = command potential |
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Term
| If membrane potential = command potential, what two currents are equal? |
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Definition
| clamp current = membrane current |
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Term
| What is the implication of no leak current existing at a certain voltage? |
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Definition
| the resting membrane potential must be that voltage |
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Term
| Is a positive driving force inward or outward? |
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Definition
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Term
| As outside [Na] decreases, the AP peak decreases - why? |
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Definition
| because decreasing sodium decreases sodium's reversal potential; since the depolarizing phase of the action potential [upstroke] is due to increasing sodium conductance, the most positive the peak could ever get is sodium's reversal potential |
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Term
| describe the 3 currents associated with a depolarization step of the squid giant axon |
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Definition
1. capacitive current (transient) inward to quickly ramp up to depolarization
2. early inward sodium current
3. later but longer outward potassium current |
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Term
| How was the ionic identity of the early current discovered? |
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Definition
| if you replace sodium with another positive ion that can't cross the membrane, you don't get the "early current" |
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Term
| How can the early current be isolated? |
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Definition
| by subtracting the remaining current in sodium-free solution from the total current recorded in the control case |
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Term
| Why could H&H not definitively identify the ion responsible for the late current (however, based on empirical observations, they speculated that it was potassium)? |
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Definition
| testing was hard because it would involve altering the cytoplasm of the cell (not the outside solution like for extracellular sodium) |
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Term
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Definition
| blocks voltage-gated sodium channels |
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Term
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Definition
| blocks voltage-gated potassium channels |
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Term
| H&H: 5 step strategy to determine the ionic basis of the action potential |
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Definition
1. measure ionic current over wide range of membrane potentials
2. isolate sodium & potassium current - H&H technique, we can use pharmacological methods
3. convert to sodium & potassium conductance (modified Ohm equations)
4. derive equations to describe sodium & potassium conductance as a function of membrane potential & of time!
5. reproduce AP with iterative algorithm |
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Term
| For what did H&H receive a Nobel Prize? |
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Definition
| their strategy to determine the ionic basis of the action potential |
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Term
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Definition
| closing of a channel due to removal of the gating signal |
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Term
| ______ acts as a voltage sensor for voltage-gated potassium channels |
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Definition
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Term
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Definition
| closing of a channel in the continued presence of the gating signal |
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Term
| describe the structure of the voltage-gated sodium channel |
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Definition
| all one long protein with a lot of subunits |
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Term
| What is the difference between inactivation & deactivation? |
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Definition
inactivation - closing of a channel in the continued presence of the gating signal
deactivation - closing of a channel due to removal of the gating signal |
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Term
| Does a potassium current deactivate or inactivate? |
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Definition
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Term
| Does a sodium channel deactivate or inactivate? |
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Definition
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Term
| What does it mean that voltage-gated sodium & potassium channel conductance have similar voltage dependencies? |
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Definition
| the relationship between how much conductance increases & increase in membrane potential is similar? |
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Term
| What is the main qualitative difference between voltage-gated sodium & potassium channels? |
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Definition
| timing of increases in conductance in response to membrane potential increase |
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Term
| If voltage-gated sodium & potassium channels are activated at similar voltages & they have similar conductance, why isn't it a wash? (Why don't the influx of sodium & efflux of potassium cancel each other out?) |
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Definition
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Term
| difference in the kinetics of voltage-gated sodium & potassium channels |
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Definition
voltage-gated sodium channels are quickly activated & then slowly inactivated
voltage-gated potassium channels are slowly activated & then deactivated |
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Term
| difference in speed of the sodium activation & inactivation gate movement |
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Definition
opening part gets to where it needs to get faster
inactivation gate starts closing at the same time activation gate starts opening, but inactivation gets to its place more slowly |
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Term
| Is the sodium activation gate normally still open when the inactivation gate is closed? |
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Definition
| yes! (but no conductance because inactivation gate is closed) |
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Term
| Hyperpolarization causes sodium inactivation gate to ______ & activation gate to ______ |
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Definition
| inactivation gate opens; activation gate closes |
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Term
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Definition
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Term
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Definition
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Term
| What was H&H's idea regarding activation & inactivation "gates"? |
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Definition
| a physical event occurred that lead to a conformational change in the channel |
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Term
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Definition
| potassium activation gate |
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Term
| Why is there a fourth order relationship between membrane potential & potassium voltage-gated channel opening? |
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Definition
| each S4 voltage sensor has to move for the channel to open |
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