Sympathetic stimulation increases pacemaker rate by enhancing which channels?

Sympathetic stimulation increases pacemaker rate by enhancing which channels?

• A. If (funny) channels
• B. Voltage-gated sodium channels in atrial myocytes
• C. Potassium leak channels
• D. Chloride channels

Answer: (A)

Sympathetic stimulation raises pacemaker rate by increasing the funny current (If) in sinoatrial node cells. Beta-adrenergic activity raises cAMP, which enhances the opening of the If channels (HCN channels). This increases the slope of diastolic depolarization, so the pacemaker reaches threshold faster and fires more quickly. The other options don’t primarily set the pacing rate: voltage-gated sodium channels in atrial myocytes drive rapid depolarization in working atrial tissue, potassium leak channels mainly set resting potential, and chloride channels do not control SA node rate.

Sympathetic stimulation raises pacemaker rate by increasing the funny current (If) in sinoatrial node cells. Beta-adrenergic activity raises cAMP, which enhances the opening of the If channels (HCN channels). This increases the slope of diastolic depolarization, so the pacemaker reaches threshold faster and fires more quickly. The other options don’t primarily set the pacing rate: voltage-gated sodium channels in atrial myocytes drive rapid depolarization in working atrial tissue, potassium leak channels mainly set resting potential, and chloride channels do not control SA node rate.