Direct interaction of Bestrophin 3 channels with Hrc calcium‐handling protein

Bestrophin 3 (Best3) is a calcium‐activated chloride channel expressed in heart and other tissues. We hypothesized that Best3 channels function in a macromolecule complex similar to other cardiac ion channels.Yeast two‐hybrid assays performed on a mouse heart library, identified histidine‐rich calcium binding protein (Hrc) as a novel binding partner of Best3. Hrc is a regulator of sarcoplasmic reticulum (SR) calcium uptake, storage and release. This interaction was further determined to involve Best3 amino acids 541–669 in the cytosolic C‐terminus of the channel and the cysteine‐rich region in mouse Hrc (amino acids 665–738 aa). Specific binding between Best3 channels and Hrc was verified by co‐immunoprecipitation using mouse heart homogenates. Confocal immunofluorescence microscopy further demonstrated a strong co‐localization of Best3 and Hrc in isolated ventricular and atrial myocytes.In this study we report that cardiac Best3 channels interact with Hrc. Calcium‐activated chloride channels play a critical role in excitation‐contraction coupling in the SR by balancing charge movement during calcium release and reuptake. The direct coupling of Best3 with Hrc suggests that Best3 channels may play a role in calcium handling in the heart by functioning as a counterion channel.