Cardiac Muscle Can Increase Its Strength of Contraction by All

Question

Cardiac muscle can increase its strength of contraction by all of the following EXCEPT A) Stretch, by increasing the sensitivity of the myofilaments to Ca²⁺ B) Increasing the size of the Ca²⁺ transients by phosphorylation of phospholamban C) Increasing recruitment of cardiomyocytes D) Increasing the size of the Ca²⁺ transients by phosphorylation of DHPR E) Increasing the size of the Ca²⁺ transients by phosphorylation of RyR2

Accepted Answer

Cardiac muscle strength of contraction can be increased by mechanisms that involve calcium handling and sensitivity, such as stretch (Frank-Starling mechanism), phosphorylation of phospholamban (which increases calcium uptake into the sarcoplasmic reticulum), and phosphorylation of DHPR and RyR2 (which affects calcium channels and receptors). However, increasing recruitment of cardiomyocytes is a mechanism that applies to skeletal muscle, not cardiac muscle, as cardiac muscle cells are interconnected and function as a single unit (functional syncytium), meaning they all contract together rather than being recruited individually.