TRIC-A Prevents Store-Overload Induced Calcium Release Through Interaction with the Cardiac Ryanodine Receptor

Abstract

TRIC-A and TRIC-B are trimeric intracellular cation channels located at the sarcoplasmic reticulum (SR) or endoplasmic reticulum (ER) of multiple cell types. These channels regulate the permeability of K ions across the SR/ER and consequently the movement of Ca ions during excitation-contraction coupling. Previously we showed that genetic ablation of TRIC led to compromised K-permeability and Ca release across the SR membrane, supporting the hypothesis that TRIC could function as counter-ion channels that allows the flow of K ions into the SR during the acute phase of Ca release. In the absence of TRIC, overload of Ca inside the ER/SR causes instability of Ca storage and release, leading to stress-induced dysfunction of multiple tissues. Spontaneous Ca waves, also called store overload-induced Ca release (SOICR) mediated by the type 2 ryanodine receptor (RyR2), evoke ventricular tachyarrhythmia in individuals with heart failure. Our biochemical studies revealed that the carboxyl-tail domain of TRIC-A could interact with the RyR channel, suggesting the possibility that TRIC-A may directly regulate the Ca release activity. We found that TRIC-A, but not TRIC-B, prevented the appearance of SOICR in HEK293 cells expressing RyR2. Cytosolic Ca measurement by Fura-2 and ER luminal Ca measurement by D1ER revealed that expression of TRIC-A in HEK293 cells could prevent overload of Ca inside the ER by targeting the RyR2 channel function. Such effect was translated into suppression of SOICR. These effects appeared to be specific for TRIC-A, as co-expression of RyR2 with TRIC-B did not affect SOICR. Together, our data suggest that functional interaction between TRIC-A and RyR can modulate the Ca release process from internal stores and regulate Ca homeostasis across the ER/SR.