Cardiac Electromechanical Coupling (DSA)

Question 1

Where do the transverse tubules invaginate the cardiac muscle cells

Answer 1

At the Z lines

Question 2

T Tubules form what with the sarcoplasmic reticulum

Answer 2

Dyads

Question 3

How does the depol. Spread to the interior of the myocytes

Answer 3

Via the T tubules

Question 4

What occurs during phase 2 of myocyte AP in regards to Ca

Answer 4

Calcium rushes into cell through Ca(L)

While this increases the C within the cell, it is not enough to cause a contraction.

Question 5

What does the Ca from the Ca(L) activate within the cell and what is the physiological purpose of this

Answer 5

Activates ryanodine receptors which cause a release of Ca from the SR

This is called ca-induced-ca release

Question 6

The calcium that enters during phase 2 and activates the ryanodine receptors is called what

Answer 6

Trigger Ca

Question 7

What two factors control how much Ca is released from the SR

Answer 7

1. The amount of Ca previously stored in the SR

2. The magnitude of the inward Ca current during phase 2 of the AP

Question 8

Once there is a drastic increase of Ca due to the Ca-induced-Ca-release, what happens next within the cardiac myocyte

Answer 8

Ca binds to Trop. C and moves the tropomyosin to allow for myosin to bing to actin and a contraction to commence

Question 9

What allows for reaccumulation of Ca from the cell and what is the purpose of this

Answer 9

Ca-ATPase

This reaccumulation causes the intracellular Ca concentration to decrease to resting levels

The Ca-ATPase also moves trigger Ca from the cell

Question 10

What two mechanisms remove trigger Ca from the cell and is their energy source

Answer 10

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

Question 11

What do positive inotropic effects do? What about negative inotropic

Answer 11

Positive - increased contractility, increased rate of tension development and peak tension

Negative - just the reverse

Question 12

Contractility depends on what

Answer 12

The amount of Ca available to allow for a contraction and cross-binding of myosin and actin.

Question 13

The amount of Ca released from the Sr depends on what two things

Answer 13

1. The magnitude of the trigger Ca influxed during phase 2 from Ca(L)
2. The amount of Ca previously stored in the SR from Ca-ATPase

Question 14

What are the three important features of sympathetic (+ inotropic) stimulation of the heart

Answer 14

1. Increased peak tension
2. Increased rate of tension development
3. Faster rate of relaxation

Question 15

How does a faster relaxation cause a (+) inotropic effect

Answer 15

Allows for a shorter contraction with stronger tension and faster refilling of Ca

Question 16

What is the receptors for sympathetic innervation of cardiac muscle

Answer 16

B1

Question 17

What two proteins are phosphorylated by PK during sympathetic stimulation and what do they do

Answer 17

1. Carcolemmal Ca Channels - increased inward Ca (trigger Ca) during the plateau phase, which increases the amount of Ca released from the SR
2. 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.

Question 18

Parasympathetic innervation acts on what receptors

Answer 18

Muscarinic with ACh

Question 19

What two things does ACh do during paraysmpathetic innervation

Answer 19

1. Decreased inward Ca current during the plateau of the AP
2. Increases Ik-Ach which shortens the duration of AP and indirectly decreases the inward Ca current by shortening the plateau phase

Question 20

When Hr increases, how does Ca behave

What is this principle called

Answer 20

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

Question 21

Cardiac glycosides are what class of drug

Answer 21

Positive inotropic agents

Question 22

What does digoxin work on in the cardiac cell? What is its ultimate goal

Answer 22

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

Question 23

Increasing the muscle length in cardiac cells increases what

Answer 23

The Ca-sensitivity of Troponin C as well as the Ca release from the SR

Question 24

The length of a single LV muscle fiber just prior to contraction corresponds to what

Answer 24

The LV EDV

Question 25

The tension of a single LV muscle fiber correlates with what

Answer 25

The tension or pressure developed by the entire LV

Question 26

Describe the Frank-Starling law

Answer 26

Increase in pre-load will = and increase in EDV an thus an increase in contractile strength and an increased SV

Question 27

Define preload

Answer 27

The end diastolic pressure which is stretching the walls of the heart to their greatest geometrical dimensions

This is due to the increased EDV

Question 28

What will an increased afterload cause

Answer 28

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