Abstract 182: Characterization of Electrophysiological and Conduction Parameters of the Heart in Trpm4-deficient Mice

TRPM4 is a Ca2+-activated non-selective cation channel that belongs to the family of the Transient Receptor Potential (TRP) ion channels. Importantly, TRPM4 is impermeable for Ca2+ and is involved in different Ca2+-dependent cell functions, such as exocytosis, contraction and cell death. Trpm4 is known to be expressed in atrial and ventricular cardiomyocytes. The interest in the functional role of TRPM4 in the heart has risen further by the discovery of Trpm4 mutations that are linked to cardiac conduction disorders, including Progressive Familial Heart Block type I (PFHBI) and Brugada Syndrome. Both gain-of-function and loss-of-function mutation were described in patients with cardiac conduction diseases. Recently, our group showed that TRPM4 plays a role during the late repolarization phase of the action potential in murine ventricular cardiomyocytes and that deletion of the Trpm4 gene leads to shorter ventricular action potentials. To characterize if deletion of Trpm4 has an effect on the conduction properties of the heart, an in depth electrophysiological study was performed in living mice. An octapolar catheter was inserted into the right atrium and ventricle of the heart to measure intracardial electrograms. The atrial-His (AH) and His-ventricular (HV) intervals were calculated and no differences were found between WT and Trpm4-deficient mice. Additionally, more detailed conduction parameters of the heart were determined by use of programmed electrical stimulation (PES) protocols. Sinus node recovery time (SNRT) was not different between WT and Trpm4-deficient mice. Effective refractory period of atrium (AERP), AV node (AVNERP) and ventricle (VERP) were in the same range in WT and Trpm4-deficient mice. Wenckebach periodicity, the parameter for AV nodal conduction, was also not different between WT and Trpm4-deficient mice. These results suggest that deletion of Trpm4 has no effects on the conduction properties of the murine heart.