The Force of Contraction of Cardiac Muscle is Typically Increased

Question

The force of contraction of cardiac muscle is typically increased by: A)An increase in Ca⁺⁺ extrusion by the Na⁺-Ca⁺⁺ antiporter in cardiac muscle. B)An increase in myosin phosphorylation in cardiac muscle. C)A decrease in cytosolic [Ca⁺⁺] in the cardiac muscle. D)β-Adrenergic stimulation of the cardiac muscle. E)Recruitment of more cardiac muscle cells.

Accepted Answer

β-adrenergic stimulation of the cardiac muscle increases the force of contraction by increasing intracellular cAMP levels, which activates protein kinase A (PKA). PKA phosphorylates multiple proteins involved in excitation-contraction coupling, leading to increased Ca2+ entry, release from the sarcoplasmic reticulum, and myofilament sensitivity to Ca2+. This ultimately results in increased force of contraction.