The Role Of Small GTPases In The Regulation Of Intracellular Transport Of Cardiac Sodium Channel (Na_v1.5)

Background:SCN5A gene encodes Na_v1.5,the pore-forming a-subunit of the cardiac voltage-gated sodium channel,which is responsible for initiation and conduction of action potentials in cardiac cell.Alterations in the normal function of Na_v1.5 have been associated with a number of cardiac arrhythmias,such as Long QT syndrome type 3(LQTS3)and Brugada syndrome.The regulation of Na_v1.5 starts with the transcription of its gene,followed by the translation of its RNA.Then it is transported from the endoplasmic reticulum(ER)to the Golgi where it undergoes post-translational modification before reaching to the sarcolemma,where it exerts its functional role.Protein trafficking is regulated by small GTPases.Normally,the small GTPases Sar1 and Arf regulate the intracellular transport of proteins in COP II and COP I vesicles,respectively.The goal of this study is to investigate the role of the small GTPases Sar1 and Arf in the regulation of Na_v1.5 trafficking.Methods:In this experiment we used HEK 293 cells as the host cells to co-express Na_v1.5 with the wild-type(WT)or mutant form of the small GTPases Sar1 and Arf.Then in order to check the effect that small GTPase has on Na_v1.5 regulation,two techniques were used to analyze the results.Western blot was performed to measure the expression level of Na_v1.5,and Confocal microscopy was used to visualize the cellular localization of Na_v1.5.Results:We found that mutant forms of Sar1 decrease Na_v1.5 expression level significantly and inhibit its localization at the cell membrane.On the other hand,Arf shows only small effect on the expression level and localization of Na_v1.5.Conclusion:This study provides evidences that Na_v1.5 intracellular transport is regulated by small GTPases,in particular Sar1.Therefore,more research should be done in the future to advance our understanding of small GTPases and their potential role and therapeutic implications in cardiac arrhythmias.