Abstract 16593: Endocytosis Pathway of Kv1.5 Channels in Atrial Cardiomyocytes

Abstract

Trafficking of ion channels in cardiomyocytes is a highly dynamic process which is determinant for shaping action potential (AP). In this study, we focused on the dynamic of Kv1.5 channel which carry the atria-specific potassium outward current involved in the repolarisation of the AP. We first investigated the endocytosis pathway for Kv1.5 channels in the atria. High resolution 3-D microscopy revealed that Kv1.5 channels are associated with clathrin vesicles in atrial myocytes but not with caveolin. Electron microscopy showed that vesicles are found both at the lateral sarcolemma and at the intercalated disc. Blockade of the clathrin pathway using sucrose or SiRNA induced an increase in IKur recorded by whole-cell patch-clamp and an accumulation of Kv1.5 channels at the sarcolemma as shown by biotinylation assay. Clathrin blockade also increased fluorescence recovery after photo bleaching of Kv1.5 channels. Altogether, these data show that Kv1.5 channels are internalized through the clathrin pathway. TIRF microscopy approach was used to follow eGFPKv1.5-Kv1.5 channels in living cells and to establish their dynamic in control and clathrin-blocked myocytes. Blockade of the clathrin pathway leads to a global increase of Kv1.5 channels at the membrane. Particle analysis revealed an accumulation of the channels into clusters and their stabilisation at the membrane. Our objective now is to investigate the involvement of the cytoskeleton in Kv1.5 channels endocytosis by using dyes staining tubulin or actin in live cells; and the fate of internalized channels at different time points by co-immunostainings with antibodies directed against the different endosomes. In conclusion, we have identified the clathrin pathway as the internalization route for Kv1.5 channel, in atrial myocytes. The blockade of this pathway modifies Kv1.5 channels dynamic at the membrane. Future work will be conducted to further investigate dynamic and fate of this atria-specific channel. This study should help understanding the constitution of the sub-membrane reservoir of repolarization that we previously described (Balse E., et al. 2009, PNAS).