Which receptor subtype is primarily found in the heart and increases heart rate and contractility?

Which receptor subtype is primarily found in the heart and increases heart rate and contractility?

• A. Alpha-1 receptors
• B. Beta-2 receptors
• C. Beta-3 receptors
• D. Beta-1 receptors

Answer: (D)

Beta-1 adrenergic receptors are the ones in the heart that drive an increase in heart rate and contractile strength. When these receptors are stimulated by sympathetic signals (epinephrine or norepinephrine), they activate a Gs protein, which boosts cAMP production. This leads to more calcium entering the cardiac cells and more calcium release from the sarcoplasmic reticulum, making the heart beat faster and with more force. That’s why activation of these receptors boosts both chronotropy (rate) and inotropy (contractility). Other receptor subtypes do different jobs—Alpha-1 mainly causes vascular smooth muscle constriction, Beta-2 promotes bronchodilation and some vasodilation, and Beta-3 is more involved in fat metabolism and bladder relaxation—so they don’t primarily govern heart rate and contractility.

Beta-1 adrenergic receptors are the ones in the heart that drive an increase in heart rate and contractile strength. When these receptors are stimulated by sympathetic signals (epinephrine or norepinephrine), they activate a Gs protein, which boosts cAMP production. This leads to more calcium entering the cardiac cells and more calcium release from the sarcoplasmic reticulum, making the heart beat faster and with more force. That’s why activation of these receptors boosts both chronotropy (rate) and inotropy (contractility). Other receptor subtypes do different jobs—Alpha-1 mainly causes vascular smooth muscle constriction, Beta-2 promotes bronchodilation and some vasodilation, and Beta-3 is more involved in fat metabolism and bladder relaxation—so they don’t primarily govern heart rate and contractility.