Figure 3. Schematic representation of the Ca²⁺ release unit model.

Trigger Ca²⁺ influx through L-type Ca²⁺ channels (LCCs) enters into the T-tubule–sarcoplasmic reticulum (T-SR) cleft (diadic space). The rise in local Ca²⁺ level promotes the opening of ryanodine receptor channels (RyRs) and Ca²⁺-dependent chloride channels (ClChs). The excess local Ca²⁺ passively diffuses out of the cleft into the cytosol, and junctional sarcoplasmic reticulum (JSR) Ca²⁺ is refilled via passive diffusion from the network sarcoplasmic reticulum (NSR).