CVS Practice Test 2025 - Free CVS Practice Questions and Study Guide

Inotropy refers to the force of heart muscle contraction, and it is primarily regulated by various mechanisms within the heart, particularly involving second messengers. The correct answer highlights the role of cAMP and IP3 in this regulation.

cAMP (cyclic adenosine monophosphate) is a vital second messenger known for its role in the signaling pathways of β-adrenergic receptors in cardiac muscle. When catecholamines (like adrenaline) bind to these receptors, it leads to an increase in cAMP levels, which in turn activates protein kinase A (PKA). This activation enhances calcium influx into the heart muscle cells during each beat, increasing the strength of contraction, hence positively affecting inotropy.

IP3 (inositol trisphosphate) plays a significant role as well, particularly in the context of certain receptor signaling pathways. When G-protein-coupled receptors are activated, lipase enzymes can produce IP3 from phosphatidylinositol bisphosphate (PIP2). IP3 binds to receptors on the endoplasmic reticulum, prompting the release of calcium ions into the cytoplasm. The increase in intracellular calcium further supports stronger contractions of the cardiac muscle.

Together, cAMP and IP3 elevate the levels of