Abstract 19049: CASK Regulates Sodium Channels Distribution and Function in Costameric Microdomain

Introduction: Proteins of the MAGUK family have emerged as key components in ion channels organization and regulation within specialized submembrane domains of cardiomyocytes. In this context, we investigated for the first time the expression, localization and function in the heart of the MAGUK protein CASK. Methods and Results: Surprisingly, no signal was detectable for CASK at intercalated discs, making CASK the first MAGUK to be excluded from these structures. On the contrary, CASK was located at the lateral membrane where it belonged specifically to the costameric dystrophin/glycoproteins complex (DGC). Since a lateral sub-population of Nav1.5 channels have been reported to interact with syntrophin, a member of DGC, we hypothesized that CASK could modulate Nav1.5 channels. Using high resolution 3-D deconvolution microscopy, we observed a co-localization of CASK and Nav1.5 in cardiomyocytes and co-IP experiments confirmed that the two proteins are in the same complex. Whole-cell patch-clamp recordings revealed a negative regulation by CASK of the sodium current INa carried by Nav1.5 channels in cardiomyocytes. Using super resolution scanning coupled to conventional cell-attached patch-clamp, we investigated the involvement of CASK on Nav1.5 function and localization in highly confined microdomains of the lateral membrane. INa was recorded in crests and T-tubules on freshly isolated cardiomyocytes obtained from adult rats injected with Adeno Associated Virus (eGFP-AAV-ShCASK or eGFP-AAV-ShScr). CASK silencing caused a drastic reduction of INa at the crest whereas it increased the current at the T-tubules suggesting that CASK retains Nav1.5 channels at the crest and prevents their clustering in T-tubules. In vivo CASK silencing in rat using an eGFP-AAV-ShCASK-injected was associated with a conduction slowing as indicated by the prolongation of the QRS duration, cardiac dilation and left ventricle systolic dysfunction. Conclusion: Taken together these results indicate that CASK is a major determinant of the organization of a subpopulation of Nav1.5 at the costamere of cardiomyocytes and that CASK-silencing induces electrical and morphological remodeling.