Which of the fol lowing contribute to pre- potential in the cardic muscleA. K +B. Transient Ca 2 +C. Longer lasting Ca 2 +D. Fast Na+E. Fast K+i-;: ,8

The pre-potential (also known as pacemaker potential) in cardiac muscle is primarily due to the slow influx of sodium ions (Na+) until the threshold is reached, which then triggers the action potential.

Here's a step-by-step breakdown:

1. The pre-potential starts at the end of the previous action potential, when the membrane potential is at its most negative. This is due to the efflux (outward flow) of potassium ions (K+).

2. The membrane potential then starts to slowly depolarize due to the slow, spontaneous influx (inward flow) of sodium ions (Na+). This is the pre-potential phase.

3. When the membrane potential reaches a certain threshold, it triggers the fast influx of calcium ions (Ca2+), which causes the membrane to depolarize rapidly and generate an action potential. This is the "spike" of the action potential.

4. After the spike, the membrane repolarizes due to the efflux of potassium ions (K+), and the cycle starts over.

So, to answer your question, the ions that contribute to the pre-potential in cardiac muscle are sodium (Na+) and potassium (K+). Calcium (Ca2+) contributes to the action potential, but not the pre-potential.