Sympathetic activation affects pacemaker activity by which change in phase 4 and Ca++ entry?

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Multiple Choice

Sympathetic activation affects pacemaker activity by which change in phase 4 and Ca++ entry?

Explanation:
Sympathetic activation speeds up pacemaker automaticity by boosting the funny current (If) and increasing Ca2+ entry during diastolic depolarization. The rise in cAMP from beta-adrenergic stimulation enhances If, and also increases L-type Ca2+ channel activity, so the diastolic depolarization (phase 4) becomes steeper and Ca2+ enters earlier. This brings the pacemaker cell to threshold more quickly, raising heart rate.

Sympathetic activation speeds up pacemaker automaticity by boosting the funny current (If) and increasing Ca2+ entry during diastolic depolarization. The rise in cAMP from beta-adrenergic stimulation enhances If, and also increases L-type Ca2+ channel activity, so the diastolic depolarization (phase 4) becomes steeper and Ca2+ enters earlier. This brings the pacemaker cell to threshold more quickly, raising heart rate.

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