4. DSA Cardiac Electrochemical Coupling

Question 1

What are the 5 steps involved in cardiac muscle contraction?

Answer 1

1. cardiac action potential
2. Ca2+ enters cell during plateau
3. Ca2+-induced Ca2+ release from SR
4. Ca2+ binds to troponin C
5. Cross-bridge cycling = TENSION
6. Alternate pathway: Cross bridge cycling can lead to Ca2+ accumulation in SR causing relaxation

Question 2

The cardiac muscle is arranged just as skeletal muscle. It is composed of sarcomeres that run from z to z line. Composed of thick and thin filaments. What makes up each?

Answer 2

Thick: myosin, globular heads with actin binding sites and ATPase activity

Thin: actin, tropomyosin, and troponin (troponin removes tropomyosin from binding site, allowing actin and mysoin to bind)

Question 3

Contraction occurs via the sliding filament model which states?

Answer 3

when cross bridges form between myosin and actin and then break, the thick and thin filaments move past each other = tension

Question 4

Transverse (T) tubules invaginate cardiac muscle cells at Z lines and function to carry action potentials to the cell interior. The T tubules form what?

Answer 4

Dyads with the sarcopaslmic reticulu, which is the site of storage and release of Ca2+ for excitation contraction coupling.

Question 5

Contactility or inotropism is the intrinsic ability of myocardial cells to develop force at a given muscle cell length. Agens that produce an increase in contractility are said to have positive inotropic effects. Positive inotropic effects increase both…?

Answer 5

the rate of tension development and the peak tension

Question 6

Agents that produce a decrease in contractability are said to have negative inotropic effects. These agents cause?

Answer 6

a decrease in both the rate of tension development and the peak tension

Question 7

Do cardiac glycosides have positive or negative inotropic effects?

Answer 7

Positive: increase rate of tension development and peak tension

Question 8

How does cross bridge cycling work?

Answer 8

It is fueled by ATP and continues as long as intracellular Ca2+ concentration is high enough to occupy the Ca2+ binding sites on the troponin C

Question 9

What important to remember about intracellular Ca2+ and the magnitude of tension developed by myocardial cells?

Answer 9

The more Ca2+ in the cell, the larger the magnitude of the tension of the cell