Which catecholamine receptor is responsible for increased heart rate?

• A. Beta-2 Receptor
• B. Beta-1 Receptor
• C. Alpha-1 Receptor
• D. Alpha-2 Receptor

Answer: (B)

Activation of beta-1 adrenergic receptors in the heart drives the tachycardic response. In the sinoatrial node, beta-1 stimulation activates Gs protein, increasing cAMP, which boosts the funny current and L-type calcium channels. This speeds up pacemaker depolarization and shortens diastole, producing a faster heart rate. The heart relies primarily on beta-1 receptors for sympathetic increases in rate, so this receptor type is the main driver of increased heart rate. Alpha-1 receptors mainly cause vasoconstriction and raise blood pressure (often with reflex effects on heart rate), alpha-2 receptors dampen sympathetic outflow, and beta-2 receptors play a smaller role in heart rate compared with beta-1.