What is the effect of beta-1 receptor activation on the heart?

What is the effect of beta-1 receptor activation on the heart?

• A. Decrease heart rate
• B. No effect
• C. Bronchodilation
• D. Increase heart rate and contractility

Answer: (D)

Activation of beta-1 receptors in the heart increases heart rate and the force of contraction. This receptor is coupled to a Gs protein, which raises intracellular cAMP. Higher cAMP activates protein kinase A, enhancing calcium entry through L-type calcium channels and increasing calcium release from the sarcoplasmic reticulum. More calcium during systole means stronger contractions (positive inotropy). It also speeds automaticity in the SA node and improves conduction through the AV node (positive chronotropy and dromotropy), together boosting cardiac output. Bronchodilation is a beta-2–mediated effect, not beta-1, so it’s not part of the heart-specific effect. Therefore, the activation of beta-1 receptors on the heart primarily increases heart rate and contractility.

Activation of beta-1 receptors in the heart increases heart rate and the force of contraction. This receptor is coupled to a Gs protein, which raises intracellular cAMP. Higher cAMP activates protein kinase A, enhancing calcium entry through L-type calcium channels and increasing calcium release from the sarcoplasmic reticulum. More calcium during systole means stronger contractions (positive inotropy). It also speeds automaticity in the SA node and improves conduction through the AV node (positive chronotropy and dromotropy), together boosting cardiac output. Bronchodilation is a beta-2–mediated effect, not beta-1, so it’s not part of the heart-specific effect. Therefore, the activation of beta-1 receptors on the heart primarily increases heart rate and contractility.