Flashcards in Holmes 2 Deck (18):
How much ATP is used to maintain Na+/K+ gradient?
33% of total energy
What does Na/K ATPase do? Electrogenic? Why? Which ion takes more energy to move?
3 Na+ out, 2 K+ in. Electrogenic because of the charge generated. Sodium needs more energy to move
Na/K ATPase in heart is receptor for ______. What is palytoxin?
Cardiac glycosides...ie. digoxin
-these inhibit the pump and increase heart contractility (treat cardiac heart arrhythmia by slowing heart rate down and increase stroke volume) -> involves calcium
palytoxin: very toxic and binds to pump allowing passive transport of Na+/K+
Does Na/K ATPase set value of resting potential?
NO, it maintains the resting potential but DOES NOT set the value of the resting potential
What sets the resting potential of a cell?
Potassium leak channels
-also called background channel because they stay open during rest and during the action potential
Vresting is closest to Vk+
What is the relation of potassium leak channels in anethesia?
Some gaseous agents such as halothane and isoflurane activate these channels and make neurons less excitable.
-ethanol can also depress excitability by increased conductance of GABA chloride channels
What are inward-rectifier potassium channels?
Another important class of leak channels. Play role in resting potential of cardiac (ventricular) myocytes
What triggers opening of voltage gated sodium channels?
Membrane depolarization. Open more readily than voltage gated potassium channels.
Describe action potential
1) resting membrane potential is mainly determined by leak potassium channels (hyperpolarized)
2) Vm reaches threshold, and fires action potential
3) Results of depolarization causes Na+ channels to be maximally open. Electrochemical gradient causes sodium to rush into the cell. Chemical gradient also favors sodium into the cell. (POSITIVE FEEDBACK)
4) the slower potassium voltage channels open and the sodium channels inactivate (shutoff by negative feedback)
Does inactivation of the voltage gated sodium and potassium channels happen inside or outside the cell?
What are the 3 distinct classes of ion channels?
1) ligand-gated: responsible for receiving synaptic input from neurotransmitters that lead to generation of AP
2) phosphorylated-gated: responsible for setting the membrane electrical potential at rest
3) voltage-gated: responsible for generation and propagation of the action potential (AP)
Where does action potential initiate?
Axon hillock (high density of voltage gated Na+ channels); this is also called zone of intitation
Remember that AP occurs by summation of signals
Temporal summation? Spatial summation?
Temporal: one signal firing twice in succession
Spatial: two diff signals fired close together
EPSP-IPSP cancellation: inhibitory and excitatory signal cancel out
The loss of conductance as an action potential progresses is a result of ________
Loss of driving force
Explain the changes in current by voltage-gated sodium channels.
1) When voltage-gated sodium channel open, inward current (positive charge) moves from outside to inside (shifts Vm towards Vna, Vm is positive inside cell)
2) Vm becomes less negative than V resting, so depolarized
3) These voltage gates also have fast inactivation gate
When we are at Vresting with all Nav channels closed, small depolarization opens some of the Nav channels and will act in positive feedback loop to open up all sodium channels
Explain the changes in current by voltage-gated potassium channels.
1) conduct outward current, positive charges from inside to out (rectification)
2) shift Vm toward Vk (towards Vresting, since Vresting is close to Vk)
3) results in hyperpolarization
4) Some Kvs also have "ball" inactivation gate like Nav (most don't)
FOLLOWS NEGATIVE FEEDBACK
To generate outward current, move potassium down concentration gradient (inside to out)
To create action potential, Kv must open after Nav channels. What 3 factors determine this?
1) Nav channels activate quicker than Kv channels
2) Nav channel activation drives positive feedback loop, Kv drives negative feedback loop
3) the V1/2 (half activation) of Kv tends to occur at more depolarized potentials compared to Nav channels (minor contribution)