Molecular Interactions of slc26a6 and CFTR in Cardiomyocytes

We have recently identified and cloned cardiac isoforms of a solute carrier, slc26a6. Importantly, we demonstrated that slc26a6 mediated electrogenic Cl-/oxalate and Cl-/HCO3- exchanges in both atrial and ventricular myocytes. Slc26a6 was previously found to interact with cystic fibrosis transmembrane conductance regulator (CFTR) chloride channels in parotid duct cells. Indeed, CFTR is also expressed in the heart. Here, we hypothesize that slc26a6 and CFTR interact in cardiomyocytes to form functional protein complexes. We examined the expression of slc26a6 and CFTR in mouse cardiomyocytes using immunocytochemistry and confocal microscopy. We found that slc26a6 and CFTR are co-expressed and co-localized in the sarcolemma of cardiomyocytes. To verify the co-localization, we employed stimulated emission depletion (STED) microscopy. The high-resolution images provided further evidence supporting the co-localization of slc26a6 and CFTR in cardiomyocytes. In slc26a6 knockoutcardiomyocytes, not only is slc26a6 expression absent but CFTR expression is significantly reduced suggesting the importance of the interaction in the membrane targeting. We further used total internal reflection fluorescence microscopy (TIRF) to study the membrane targeting of slc26a6 (or CFTR) in the absence or presence of CFTR (or slc26a6). Indeed, the membrane targeting of slc26a6 (or CFTR) is enhanced by the co-expression of its putative interacting partner. Additionally, patch-clamp recordings demonstrate that the anion exchange activities of slc26a6 were enhanced by the activation of CFTR. In conclusion, slc26a6 and CFTR are co-expressed and co-localized in cardiomyocytes forming functional protein complexes. Activation of CFTR enhances the function of slc26a6. Moreover, the molecular interaction between slc26a6 and CFTR is essential for their membrane targeting. This new insight helps to pave the way for understanding the novel roles of slc26a6 and CFTR in the regulation of cardiac pH and excitability.Funded by AHA Western States Affiliate Beginning Grant-in-Aid (14BGIA18870087 to XZ).