January 8, 2016 - Excitation/Contraction

Question 1

Ryanodine Receptors

Answer 1

Receptors on the sarcoplasmic reticulum that bind calcium.

Not really receptors as much as calcium-induced calcium channels.

Causes a further massive release of calcium from the sarcoplasmic reticulum, which will bind to Troponin C, opening myosin binding sites on actin and leading to a muscle contraction.

Question 2

SERCA2a

Answer 2

Sarco/Endoplasmic Reticulum Ca^{<strong>2</strong>+}-ATPase

Responsible for pumping calcium ions back into the sarcoplasmic reticulum from the cytoplasm at the expense of ATP.

Question 3

ATP and Muscle Contraction

Answer 3

ATP is needed for SERCA to pump calcium back into the SR.

ATP is needed for the myosin head to bind a new ATP.

In energy depleted states (ischemia), the myocardium is stiffened.

Question 4

B1-Andrenergic Effects

Answer 4

When epinephrine binds to B-receptors, it activates a cellular cascade and results in the phosphorylation of phospholambin by PKA. When phosphorylated, phospholambin has a reduced ability to bind to SERCA which allows SERCA to have increased activity.

This results in increased squeezing of the heart.

Question 5

Heart Failure and Calcium

Answer 5

Heart failure often has calcium overload as a common feature. This results in decreased contractile performance.

This can be due to decreased levels of SERCA2a, Ryanodine leaks, an increase in Na/Ca exchange, or decreased B1-Andrenergic receptors.