Answer:
Calcium ions.
Explanation:
The generation of the action potential helps in the transfer of information to the different body parts. This potential occurs to the difference in membrane potential inside and outside of the cell.
The sarcoplasmic reticulum is the homologous to the endoplasmic reticulum of the cells. The sarcoplasmic reticulum contains calcium ions in it and releases the stored calcium ions on the generation of the action potential. This calcium ion is important for the action of the actin and myosin.
Thus, the correct answer is option (D).
