Ionic Basis Of The Cardiac Action Potential Flashcards
In regards to a Na+ ion channel: how many transmembrane segments are there per alpha subunit
24 transmembrane segments per alpha subunit
In regards to a Na+ ion channel: how many alpha subunits are there per Na+ channel
1 alpha subunit per Na+ channel
How is the Na+ ion channel coded by genes
Coded as one long strand
In regards to a K+ ion channel: how many transmembrane segments per alpha subunit
6 transmembrane segments per alpha subunit
In regards to a K+ ion channel: how many alpha subunits per K+ channel
4 alpha subunits per K+ channel
How do genes code for a K+ ion channel
Code in 4 separate sections and cell puts together
Role of beta subunits in ion channels?
Modify membrane expression and modify behaviour of alpha subunits
What are the auxiliary (accessory-other than alpha) subunits of the Ca2+ ion channel
Beta subunit
Gamma subunit
Alpha2-delta subunit (joined by s-s bond)
Ohms law equation and the current equation we derive from it
Ohms law: V= I x R
Derive: I= V x G
* R= 1/G *
What does G stand for
Conductance of ions
What makes up delta V (voltage)
Delta V= Vm-Eion
Vm- membrane potential
Eion- equilibrium potential for that ion
What forces act on an ion when it moves?
Electrical gradient
Concentration gradient
together its called the electrochemical gradient
How does the nernst equation change units?
Turns chemical units into electrical units
Provide the nernst equation
Eion = (RT)/(zF)*ln(ion-out/ion-in)
What are the equilibrium potentials of: K, Na, Ca
Ek= -90 mV
Ena= +65 mv
Eca= +120 mV at rest AND +90 mV during contraction
At rest what ions have the most conductance (G) through the membrane
Potassium
What phenomenon does the goldman-hodgkin-katz equation explain
The membrane potential (Vm) is closest to the equilibrium potential of the ion that permeates the membrane most freely (ex. Only K permeates, Vm= Ek)
What does the conductance of an ion depend on
If channel is open
Number of ion channels
When you are depolarizing the membrane, what charge is moving and what direction
Positive charge is moving into the cell
What events occur in skeletal muscle that do not occur in cardiac muscle and why do they not occur in cardiac muscle
- Variable recruitment of muscle fibres
- Frequency dependence- summation and tetanus
Cant occur because: - Functional syncytium so 100% recruitment with every beat
- No summation or tetany due to long AP duration
Name the 5 phases of cardiac action potential
4- resting membrane potential
0- depolarization
1- rapid repolarization
2- plateau
3- repolarization
What channels control phase 4 and what direction do the ions flow
4- Resting membrane potential
Kir2.1 channels
Ik1 current flows out
What channels control phase 0 and what direction do ions flow
0- depolarization
Nav1.5 channels
Ions flow into cell
What channels control phase 1 and what direction do ions flow
1- rapid repolarization (epicardium, surface of myocyte)
Kv4.3 channels
Transient K+ current out of the cell (Ik,to current)