B1 receptor activation on the heart produces which effect?

B1 receptor activation on the heart produces which effect?

• A. Negative inotropy
• B. Lusitropic effect-enhanced ventricular relaxation
• C. Increased conduction velocity
• D. No effect

Answer: (B)

β1 receptor activation in the heart boosts signaling through the Gs–cAMP–PKA pathway, which enhances calcium handling. This not only increases contractility but also speeds up relaxation by phosphorylating phospholamban, which relieves its inhibition of SERCA and speeds calcium uptake into the sarcoplasmic reticulum during diastole. The result is a faster, more complete ventricular relaxation—a lusitropic effect. While β1 stimulation can also raise conduction velocity and contractility, the described lusitropic change is a distinct and important effect of β1 activation, making it the best match for the question.

β1 receptor activation in the heart boosts signaling through the Gs–cAMP–PKA pathway, which enhances calcium handling. This not only increases contractility but also speeds up relaxation by phosphorylating phospholamban, which relieves its inhibition of SERCA and speeds calcium uptake into the sarcoplasmic reticulum during diastole. The result is a faster, more complete ventricular relaxation—a lusitropic effect. While β1 stimulation can also raise conduction velocity and contractility, the described lusitropic change is a distinct and important effect of β1 activation, making it the best match for the question.