Cardiac Electromechanical Coupling (DSA) Flashcards
Where do the transverse tubules invaginate the cardiac muscle cells
At the Z lines
T Tubules form what with the sarcoplasmic reticulum
Dyads
How does the depol. Spread to the interior of the myocytes
Via the T tubules
What occurs during phase 2 of myocyte AP in regards to Ca
Calcium rushes into cell through Ca(L)
While this increases the C within the cell, it is not enough to cause a contraction.
What does the Ca from the Ca(L) activate within the cell and what is the physiological purpose of this
Activates ryanodine receptors which cause a release of Ca from the SR
This is called ca-induced-ca release
The calcium that enters during phase 2 and activates the ryanodine receptors is called what
Trigger Ca
What two factors control how much Ca is released from the SR
- The amount of Ca previously stored in the SR
2. The magnitude of the inward Ca current during phase 2 of the AP
Once there is a drastic increase of Ca due to the Ca-induced-Ca-release, what happens next within the cardiac myocyte
Ca binds to Trop. C and moves the tropomyosin to allow for myosin to bing to actin and a contraction to commence
What allows for reaccumulation of Ca from the cell and what is the purpose of this
Ca-ATPase
This reaccumulation causes the intracellular Ca concentration to decrease to resting levels
The Ca-ATPase also moves trigger Ca from the cell
What two mechanisms remove trigger Ca from the cell and is their energy source
Ca-ATPase and Ca-Na exchange
Ca-ATPase uses ATP while Ca-Na pumps Ca against it’s gradient and uses the force of inward Na gradient to power it
What do positive inotropic effects do? What about negative inotropic
Positive - increased contractility, increased rate of tension development and peak tension
Negative - just the reverse
Contractility depends on what
The amount of Ca available to allow for a contraction and cross-binding of myosin and actin.
The amount of Ca released from the Sr depends on what two things
- The magnitude of the trigger Ca influxed during phase 2 from Ca(L)
- The amount of Ca previously stored in the SR from Ca-ATPase
What are the three important features of sympathetic (+ inotropic) stimulation of the heart
- Increased peak tension
- Increased rate of tension development
- Faster rate of relaxation
How does a faster relaxation cause a (+) inotropic effect
Allows for a shorter contraction with stronger tension and faster refilling of Ca
What is the receptors for sympathetic innervation of cardiac muscle
B1
What two proteins are phosphorylated by PK during sympathetic stimulation and what do they do
- Carcolemmal Ca Channels - increased inward Ca (trigger Ca) during the plateau phase, which increases the amount of Ca released from the SR
- Phospholamban - regulates Ca-ATPase. When phosphorylated, activates Ca-ATPase resulting in greater uptake and storage of Ca by the SR which causes faster relaxation and an increase in the amount of Ca stored for subsequent beats.
Parasympathetic innervation acts on what receptors
Muscarinic with ACh
What two things does ACh do during paraysmpathetic innervation
- Decreased inward Ca current during the plateau of the AP
- Increases Ik-Ach which shortens the duration of AP and indirectly decreases the inward Ca current by shortening the plateau phase
When Hr increases, how does Ca behave
What is this principle called
There is more AP per unit time, and thus an increase in total amount of Trigger Ca and thus more Ca to activate muscle contraction
Called the Positive staircase effect or the Bowditch staircase
Cardiac glycosides are what class of drug
Positive inotropic agents
What does digoxin work on in the cardiac cell? What is its ultimate goal
Inhibits the Na/K ATPase pump. This increases intracellular Na concentration and thus slows down the Na-Ca exchanger, causing less Ca to be sent out and more to be available to allow for more cardiac contraction and a positive inotropic effect
Increasing the muscle length in cardiac cells increases what
The Ca-sensitivity of Troponin C as well as the Ca release from the SR
The length of a single LV muscle fiber just prior to contraction corresponds to what
The LV EDV
The tension of a single LV muscle fiber correlates with what
The tension or pressure developed by the entire LV
Describe the Frank-Starling law
Increase in pre-load will = and increase in EDV an thus an increase in contractile strength and an increased SV
Define preload
The end diastolic pressure which is stretching the walls of the heart to their greatest geometrical dimensions
This is due to the increased EDV
What will an increased afterload cause
This will cause an increased AoP and a decrease in the velocity of shortening myocytes and thus an increase in work of the LV which is not good
This happens in HTN
