Which type of action potential contains Na+ channels, pacemaker or ventricular?

Ventricular action potentials primarily involve the rapid influx of sodium ions (Na+) through sodium channels during the depolarization phase. This characteristic is a defining feature of the action potentials seen in ventricular myocytes (heart muscle cells), allowing for the rapid conduction of electrical impulses that trigger contraction. The influx of Na+ is essential for quick depolarization, leading to a strong and coordinated contraction of the heart muscle.

In contrast, pacemaker action potentials (found in the sinoatrial node and other nodes in the heart) rely mainly on calcium channels for depolarization. These cells have spontaneous rhythmic firing due to the gradual influx of positively charged ions primarily through calcium channels, rather than sodium channels. The lack of reliance on Na+ influx during the initial phases of depolarization in pacemaker cells distinguishes them from ventricular action potentials.

Therefore, focusing on the characteristics of sodium channels in the context of action potentials indicates that they are a key component of ventricular action potentials, making this the correct choice.