What is the resting membrane potential (RMP) of SA nodal cells?

What is the resting membrane potential (RMP) of SA nodal cells?

• A. Approximately -60 mV
• B. Approximately -70 mV
• C. Approximately -90 mV
• D. 0 mV

Answer: (A)

SA node cells are specialized pacemaker cells that don’t sit on a highly negative, stable resting potential like working cardiac muscle. Instead, they have a less negative baseline around -60 mV, which is the starting point for the gradual depolarization (pacemaker potential) that drives automatic firing. This tendency to drift toward threshold due to the funny current (If) and other ion conductances explains why SA nodal tissue can initiate impulses spontaneously. The -60 mV figure sits between the more negative resting potentials of ventricular/atrial myocytes (roughly -85 to -90 mV) and zero, reflecting its unique role in setting the pace of the heart. Therefore, approximately -60 mV is the best representation of the SA node’s resting state.

SA node cells are specialized pacemaker cells that don’t sit on a highly negative, stable resting potential like working cardiac muscle. Instead, they have a less negative baseline around -60 mV, which is the starting point for the gradual depolarization (pacemaker potential) that drives automatic firing. This tendency to drift toward threshold due to the funny current (If) and other ion conductances explains why SA nodal tissue can initiate impulses spontaneously. The -60 mV figure sits between the more negative resting potentials of ventricular/atrial myocytes (roughly -85 to -90 mV) and zero, reflecting its unique role in setting the pace of the heart. Therefore, approximately -60 mV is the best representation of the SA node’s resting state.