Final answer:
Depolarization down a T-tubule leads to the activation of Ryanodine Receptors (RyR), which are calcium release channels on the sarcoplasmic reticulum, resulting in the release of Ca2+ into the sarcoplasm.
Step-by-step explanation:
The question pertains to the process of muscle contraction, specifically the role of different proteins in the depolarization of the T-tubule and the subsequent release of calcium from the sarcoplasmic reticulum (SR). When an action potential travels down a T-tubule, it triggers the opening of calcium channels in the membrane of the adjacent SR, which leads to the release of Ca2+ into the sarcoplasm. The correct answer is B) RyR, which stands for Ryanodine Receptor. The RyR is a calcium release channel on the SR that is activated as a result of the action potential that travels down the T-tubules. Therefore, the depolarization down a T-tubule results in the activation of Ryanodine Receptors (RyR).