Eps15 homology domain-containing protein 3 regulates cardiac T-type Ca²⁺ channel targeting and function in the atria

Proper trafficking of membrane-bound ion channels and transporters is requisite for normal cardiac function. Endosome-based protein trafficking of membrane-bound ion channels and transporters in the heart is poorly understood, particularly in vivo. In fact, for select cardiac cell types such as atrial myocytes, virtually nothing is known regarding endosomal transport. We previously linked the C-terminal Eps15 homology domain-containing protein 3 (EHD3) with endosome-based protein trafficking in ventricular cardiomyocytes. Here we sought to define the roles and membrane protein targets for EHD3 in atria. We identify the voltage-gated T-type Ca²⁺ channels (Ca_V3.1, Ca_V3.2) as substrates for EHD3-dependent trafficking in atria. Mice selectively lacking EHD3 in heart display reduced expression and targeting of both Ca_v3.1 and Ca_V3.2 in the atria. Furthermore, functional experiments identify a significant loss of T-type-mediated Ca²⁺ current in EHD3-deficient atrial myocytes. Moreover, EHD3 associates with both Ca_V3.1 and Ca_V3.2 in co-immunoprecipitation experiments. T-type Ca²⁺ channel function is critical for proper electrical conduction through the atria. Consistent with these roles, EHD3-deficient mice demonstrate heart rate variability, sinus pause, and atrioventricular conduction block. In summary, our findings identify Ca_V3.1 and Ca_V3.2 as substrates for EHD3-dependent protein trafficking in heart, provide in vivo data on endosome-based trafficking pathways in atria, and implicate EHD3 as a key player in the regulation of atrial myocyte excitability and cardiac conduction.