Which ion has a greater concentration inside the cardiac pacemaker cells contributing to the resting membrane potential?

The resting membrane potential of cardiac pacemaker cells is primarily influenced by the concentration of potassium ions. In these cells, there is a higher concentration of potassium inside compared to the outside environment. This concentration gradient is crucial because it leads to the movement of potassium ions out of the cell through potassium channels, causing a negative charge inside the cell relative to the outside, which establishes the resting membrane potential.

Potassium's role is essential in maintaining this potential because the resting membrane potential is predominantly determined by the permeability of the cell membrane to potassium ions at rest. When potassium moves out of the cell, it results in a more negative internal environment, which is vital for the proper functioning of pacemaker cells in generating action potentials and controlling the heart rate.

In contrast, sodium ions are found in greater concentrations outside cardiac pacemaker cells and tend to move into the cell, which depolarizes the membrane but does not contribute to the resting potential as significantly as potassium does. Calcium and bicarbonate ions also play various roles in cardiac function but are not the primary contributors to the established resting membrane potential in these cells.