The contractility of the heart can be modified through the release of norepinephrine from sympathetic neurons. A cAMP-mediated signal transduction cascade is activated that activates a protein kinase
List and describe the four ways that a protein kinase can affect the contractility of the heart.
Answer: i. Phosphorylation of L-type calcium channels on the cell membrane allows increased Ca2+ into the cell in response to depolarization.
ii. Phosphorylation of proteins in the membrane of the sarcoplasmic reticulum causes it to release more Ca2+ in response to an action potential.
iii. Phosphorylation of myosin increases the rate of myosin ATPase, increasing the rate of cross-bridge cycling and the speed of muscle contraction
iv. Phosphorylation of the sarcoplasmic reticulum Ca2+ ATPase enhances Ca2+ reuptake into the sarcoplasmic reticulum, increasing the rate of relaxation.
v. All together, these four mechanisms cause the cardiomyocytes to contract faster and more strongly in response to sympathetic stimulation, increasing the stroke volume of the heart.
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