CELLULAR NEUROPHYSIOLOGY CONSTANCE HAMMOND 2. THE SODIUM ACTION POTENTIAL Video 2-1: Observations and hypotheses
Sodium action potential 1
Observations 2 Patch clamp recording whole-cell configuration current-clamp mode Action potential = strong depolarization sudden short all or none with a threshold potential
Action potential: ionic mechanisms 3 K + channel blocker Na + channel blocker Are Na + and K + ions the only ions involved in the action potential?
Action potential: ionic mechanisms 4 Adding Ca 2+ channel blockers no change Removing extracellular Ca 2+ ions no change Adding a Cl - channel blocker no change Replacing extracellular Cl - ions with non permeant anions no change Ca 2+ and Cl - ions: not involved in sodium action potential
Action potential: ionic mechanisms 5 Hypotheses: K + ions participate in the repolarization phase Na + ions participate in the depolarization phase or in both depolarization and repolarization phases
Action potential: underlying ionic currents 6 Patch clamp recording whole-cell configuration voltage-clamp mode
Action potential: underlying ionic currents 7 Patch clamp recording whole-cell configuration voltage-clamp mode + TTX
Action potential: underlying ionic currents 8 Patch clamp recording whole-cell configuration voltage-clamp mode + TEA
Action potential: underlying ionic currents 9 Patch clamp recording whole-cell configuration voltage-clamp mode a TTX-sensitive Na + current is responsible for the depolarization phase a TEA-sensitive K + current is responsible for the repolarization phase
Action potential: underlying ionic currents 10 1. Why does the Na + current appear first? Why is it inward and short? 2. Why is the K + current delayed, outward, and longer?
Take home message 11 The action potential is all or none, sudden and short Na + and K + currents underlie the action potential
CELLULAR NEUROPHYSIOLOGY CONSTANCE HAMMOND 2. THE SODIUM ACTION POTENTIAL Video 2-2: Sodium channel and unitary current
The voltage-sensitive Na + channel 12
Unitary Na + current (i Na ) 13 cell-attached configuration (a single channel) voltage-clamp mode mm +
Unitary Na + current (i Na ) 14 Na + current amplitude: stable (at a given voltage) Latency and duration: variable Maximum one opening per voltage step 3 channel states: closed open inactivated
Unitary Na + current (i Na ) 15 In which direction does the Na + current flow? C O
CELLULAR NEUROPHYSIOLOGY CONSTANCE HAMMOND 2. THE SODIUM ACTION POTENTIAL Video 2-3: Total sodium current
Total Na + current (I Na ) 16 whole-cell configuration voltage-clamp mode + K + and Ca 2+ channel blockers At -30 mv, the total Na + current is inward. It activates and inactivates quickly.
Total Na + current (I Na ) 17
Take home message 18 Na + channels rapidly open from a depolarization threshold and then rapidly inactivate. They close when the membrane repolarizes. The total Na + current is responsible for the depolarization phase of the action potential.
CELLULAR NEUROPHYSIOLOGY CONSTANCE HAMMOND 2. THE SODIUM ACTION POTENTIAL Video 2-4: Potassium channel and unitary current
The action potential K + channel 19
Unitary K + current (i K ) 20 outside-out configuration voltage-clamp mode + Na + and Ca 2+ channel blockers a positive current = positively-charged ions move out of the cell
Unitary K + current (i K ) 21 Delayed activation K + current amplitude: stable at a given voltage Variable opening duration Multiple openings per voltage step 2 channel states: closed open Does not inactivate!
Unitary K + current (i K ) 22
CELLULAR NEUROPHYSIOLOGY CONSTANCE HAMMOND 2. THE SODIUM ACTION POTENTIAL Video 2-5: Total potassium current
Total K + current (I K ) 23 whole-cell configuration voltage-clamp mode The total potassium current is an outward current that activates with a delay and does not inactive.
Total K + current (I K ) 24 whole-cell configuration voltage-clamp mode
Take home message 25 K + channels open with a delay in response to membrane depolarization. They close when the membrane repolarizes. The total K + current is responsible for the repolarization phase of the action potential.
CELLULAR NEUROPHYSIOLOGY CONSTANCE HAMMOND 2. THE SODIUM ACTION POTENTIAL Video 2-6: Conclusion
Overview of the sodium action potential 26 1. In which state are the Na + and K + channels during the different phases of the action potential?
Overview of the sodium action potential 27 2. Where is the action potential initiated?
Overview of the sodium action potential 28 3. How does the action potential propagate along the axon? t 0 t 1 t 2
Overview of the sodium action potential 29 3. How does the action potential propagate along the axon?
Overview of the sodium action potential 30 dendrite afferents axon soma initial segment myelin node of Ranvier The action potential is initiated at the axon initial segment It backpropagates to the soma and then stops It propagates without decrement down to the axon terminals, where it triggers neurotransmitter release axon terminals
CELLULAR NEUROPHYSIOLOGY CONSTANCE HAMMOND Professor Constance Hammond Project manager Isabelle Virard Graphic designer Géraldine Fohr Movie director Marine Chabrolin Music Tetoma - Hicham Chahidi Translation Atenao 2016