A typically prolonged transient increase in intracellular Ca²⁺ concentration, which is detected by a Ca²⁺ indicator. The increased Ca²⁺ levels are due to Ca²⁺ release from intracellular Ca²⁺‐stores and to Ca²⁺ influx from the external medium.

 IP₃ Receptor

 Ryanodine Receptor

 Non-selective Cations Channels

 TRP Channels