During the depolarization phase of the nodal action potential, the cardiac myocyte membrane is most permeable to _-• Kt Na+• Ca2+

During the depolarization phase of the nodal action potential, the cardiac myocyte membrane is most permeable to Ca2+.

Here's the step by step process:

1. The action potential in cardiac myocytes begins with the opening of voltage-gated Na+ channels, causing a rapid influx of Na+ ions. This is the initial depolarization phase.

2. However, these Na+ channels quickly inactivate and close, stopping the influx of Na+ ions.

3. At the same time, voltage-gated Ca2+ channels open up. These channels are slower to open and close than the Na+ channels.

4. The Ca2+ ions entering the cell cause further depolarization, and this is the phase where the membrane is most permeable to Ca2+ ions.

5. The Ca2+ channels eventually close and K+ channels open, allowing K+ ions to leave the cell. This causes repolarization and returns the membrane potential to its resting state.

6. The K+ channels then close, ready for the next action potential.

So, during the depolarization phase of the nodal action potential, the cardiac myocyte membrane is most permeable to Ca2+.