TRIC channels are essential for Ca²⁺ handling in intracellular stores

Cell signalling requires efficient Ca²⁺ mobilization from intracellular stores through Ca²⁺ release channels, as well as predicted counter-movement of ions across the sarcoplasmic/endoplasmic reticulum membrane to balance the transient negative potential generated by Ca ²⁺ release. Ca²⁺ release channels were cloned more than 15 years ago, whereas the molecular identity of putative counter-ion channels remains unknown. Here we report two TRIC (trimeric intracellular cation) channel subtypes that are differentially expressed on intracellular stores in animal cell types. TRIC subtypes contain three proposed transmembrane segments, and form homo-trimers with a bullet-like structure. Electrophysiological measurements with purified TRIC preparations identify a monovalent cation-selective channel. In TRIC-knockout mice suffering embryonic cardiac failure, mutant cardiac myocytes show severe dysfunction in intracellular Ca²⁺ handling. The TRIC-deficient skeletal muscle sarcoplasmic reticulum shows reduced K⁺ permeability, as well as altered Ca ²⁺ 'spark' signalling and voltage-induced Ca²⁺ release. Therefore, TRIC channels are likely to act as counter-ion channels that function in synchronization with Ca²⁺ release from intracellular stores.