What event occurs as a result of T tubule depolarization in muscle contraction?

During muscle contraction, depolarization of the T tubules plays a crucial role in the process of excitation-contraction coupling. When the muscle cell membrane, including the T tubules, depolarizes, it generates an action potential that spreads along the T tubules. This depolarization is critical for the subsequent release of calcium ions (Ca²⁺) from the sarcoplasmic reticulum (SR), which is a specialized endoplasmic reticulum in muscle cells that stores calcium.

The action potential triggers voltage-sensitive proteins in the T tubules, which are mechanically coupled to calcium release channels in the sarcoplasmic reticulum. As a result, calcium is released into the cytosol. This increase in intracellular calcium concentration is what ultimately initiates the contraction of muscle fibers, allowing the myofilaments (actin and myosin) to interact and produce muscle contraction.

Thus, the event that occurs as a result of T tubule depolarization is the release of calcium from the sarcoplasmic reticulum. This release is essential for the initiation of muscle contraction and is a key link between the electrical signal and the mechanical response of the muscle.