Which receptor increases heart rate and pump force?

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Multiple Choice

Which receptor increases heart rate and pump force?

Beta-1 adrenergic receptors on the heart are the main mediators of increasing both heart rate and the strength of contraction during sympathetic activation. When norepinephrine or epinephrine binds to these receptors, it activates Gs proteins, which stimulate adenylyl cyclase to raise cAMP levels. The rise in cAMP activates protein kinase A, leading to more calcium entering the cardiac muscle cells during each beat and greater calcium release from the sarcoplasmic reticulum. This makes each beat stronger (positive inotropy) and also speeds up the rate of firing in the SA node (positive chronotropy), so both heart rate and pumping force go up. Alpha-1 receptors, by contrast, mainly cause vasoconstriction in vascular smooth muscle and don’t directly boost heart contractility. Beta-2 receptors can contribute to some cardiac and vascular effects but are not the primary driver of increased heart rate and force—that role belongs to beta-1. Dopamine receptors influence renal perfusion and other pathways rather than directly increasing cardiac rate and contractility.

Beta-1 adrenergic receptors on the heart are the main mediators of increasing both heart rate and the strength of contraction during sympathetic activation. When norepinephrine or epinephrine binds to these receptors, it activates Gs proteins, which stimulate adenylyl cyclase to raise cAMP levels. The rise in cAMP activates protein kinase A, leading to more calcium entering the cardiac muscle cells during each beat and greater calcium release from the sarcoplasmic reticulum. This makes each beat stronger (positive inotropy) and also speeds up the rate of firing in the SA node (positive chronotropy), so both heart rate and pumping force go up.

Alpha-1 receptors, by contrast, mainly cause vasoconstriction in vascular smooth muscle and don’t directly boost heart contractility. Beta-2 receptors can contribute to some cardiac and vascular effects but are not the primary driver of increased heart rate and force—that role belongs to beta-1. Dopamine receptors influence renal perfusion and other pathways rather than directly increasing cardiac rate and contractility.

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