Action Potential Generation Flashcards
(26 cards)
What are four examples of “use dependent” blockade anesthetics. What is their mechanism?
They bind better to open voltage-gated Na channels.
- cocaine
- procaine
- lidocaine.
- tetracaine
Name three external blockers of Na+ channels and where they come from. What is their mechanism?
These bind to external sites to block the Na channel.
NaTS MuC(k things up)
Tetrodotoxin - from puffer fish Saxitoxin - from dinoflagellates that produce the red tide Mu conotoxin - from marine snail - only blocks Na channels of skeletal muscle, but not in cardiac muscle or neurons
How you alter the activity of voltage-gated Na channels
block the channel
competitive inhibition with a drug that binds better to the open channel
keep Na channel open longer
How do promotoers of Na channel activity alter Na channel kinetics?
- increased duration of channel opening
2. enhanced opening under voltage conditions in which channels are normally closed or inactivated
Which four neurotoxins are promoters of Na channel activity and where do they come from? What is their mechanism?
VERy BAd Perverted BREthren
(plants are eaten by frogs while crysthanemums are the food for dinos)
veratridine - plant alkaloid batrachotoxin - alkaloid from tropical frogs pyrethins - natural plant insecticide from chrysanthemums brevetoxins - from dinoflagellates (in red ride?)
These neurotoxins produce a longer duration of Na channel opening and enhanced opening under voltage conditions in which channels are usually closed or inactivated.
Name four major types of voltage-gated K channels
Delayed outward rectifiers, Inward rectifier (anomalous rectifiers), Transient outward rectifiers (A-type currents), Ca2+-activated K currents
What are the properties of delayed outward rectifiers?
- Slow to activate
- Outward movement of K+ at depolarized potentials
- Inactivates very slowly (seconds to minutes)
BLOCKED BY tetraetylammonium (TEA)
What are properties of Inward rectifiers/anomalous rectifiers? What are they blocked by?
- inward movement of K+
- little outward movement at depolarized potentials
- Prevent excessive loss of K+ during prolonged depolarizations (e.g. cardiac action potential)
BLOCKED BY Tertiapin (honey bee venom)
What are properties of Transient outward rectifiers (A-type currents)? What blocks A-type currents/Transient outward rectifiers?
- activate and inactivate very fast
- activate at more negative potentials than other K channels
- activated during afterhyperpolarization phase
- can control rate of spontaneous action potential discharge (e.g. in cardiac muscle responsible for phase 1 rapid repolarization
BLOCKED BY 4-aminopyridine
What are properties of Ca2+-activated K currents? What blocks Ca2+-activated K currents?
very common type of K channel, depolarization or an increase in intracellular Ca2+ opens these channels
BLOCKED BY: Apamin (component of honey bee venom); Charybdotoxin (component of scorpion venom)
What are components of honey bee venom?
Apamin (blocks Ca2+ activated K current channels)
and
Tertiapin (blocks inward rectifier K channels)
What is electrotonic conduction?
When the local response shows decremental conduction– in that the response is smaller and slower away from the site of stimulus.
What does the time constant represent?
time constant = tau = R_m*C_m
The time constant is the time course of the potential to change to a value of 63% or fall to 37% of its peak value
What is the length constant formula and what does the length constant represent?
length constant = lambda = sqrt(r_m/r_i)
The length constant is the distance at which a potential has fallen to 37% of it’s original value.
larger the R_m && smaller the R_i = longer lambda
What are characteristic properties of an action potential?
- large, self sustaining potential change
2. propagation without decrement away from site of stimulus
What are properties of ionic conductance (g_i)?
- It is the inverse of resistance
2. The greater the number of channels open the higher the conductance.
What type of channel is a voltage-gated K channel in an action potential?
Delayed rectifier channel (slow to open)
What factors affect threshold?
- desntiy of Na channels
- availability of Na channels that can be activated
- concentration of divalent cations (esp. Ca2+), which alter the threshold.
How does calcium ions (hyocalcemia and hypercalcemia) alter threshold? What does this result in?
Hypocalcemia (the lack of Ca2+ ions) reduce the threshold
- Reults: hyperexcitability and spontaneous muscle contractions
Hypercalcemia (the increase in Ca2+ ions) increase the threshold further away from resting potential.
- Results: hypoexcitability and muscle weaknes
How does an action potential produced during the relative refractory period compare to a normal action potential?
The action potential produced during the relative refractory period will have a reduced amplitude and slower rate of rise compared to one produced at resting conditions.
What is Overshoot and what causes it?
Overshoot is a reverse in cell polarity by the peak potential exceeding 0mV and caused by E_m approaching E_Na and/or E_Ca
Describe cardiac action potentials
- Initial fast rising phase (due to fas Na channels)
- prolonged plateau phase (due to slow L-type Ca channels)
- repolarization due to closing of slow channels and very delayed reopening of K channels
Describe smooth muscle action potentials
- longer duration than skeletal muscle action potential
- rising phase due to slow, L-type Ca channels (and sometimes Na channels)
- repolarization due to closing of slow channels and opening of K channels
What does Na/K pump have to do with action potentials?
NOTHING! The Na-K pump has nothing to do with the action potential except setting up the stage to allow the action potential to occur
