Investigating the interactions of auxillary subunits with the Nav1.5 channel

Project Summary/Abstract Within the years 2013 to 2016, 6.2 million patients were diagnosed with heart failure in the United States. Heart failure has multiple causes, and many fatal cases include patients being predisposed to arrhythmias. One mechanism for triggering a pro-arrhythmic state are changes cardiac action potential such as the prolongation of the depolarization. The main contributor of this rapid depolarization is the ionic current supplied by the Nav1.5 voltage gated sodium channel within the human heart. In addition, there are multiple subunits that interact with the channel in a physiological setting including the subunits of intracellular fibroblast growth factor (FGF) 12A, FGF12B, and calmodulin (CaM). In preliminary data, it has been shown that FGF12A is upregulated in the left ventricle in failing hearts and that FGF12B is the most prevalent FGF isoform in the human heart. Both FGF12A, FGF12B and CaM have shown to alter the inactivation of the Nav1.5 channel through modulation of the DIII and DIV voltage sensing domains (VSD). However, there is no research as to the combined effects of these subunits and their potential to synergistically modulate the Nav1.5 VSDs. As the DIII and DIV VSDs are modulated by these proposed subunits, it can be hypothesized that the efficacy of class 1b anti-arrhythmic drugs are also affected by the proposed subunits. These preliminary findings confer to the two hypotheses: (1) combinations of modulating subunits bound to Nav1.5 can collectively alter gating to disrupt activation and inactivaiton and (2) the subunits of FGF12A, FGF12B, and CaM will alter the interaction of efficacy of class 1b anti-arrhythmic drugs. To support these hypotheses, three aims were created. Aim 1 will focus on determining the biophysical changes the combined subunits have on the Nav1.5 VSDs. The aim will be accomplished with the use of voltage clamp fluorometry to examine the changes in the activation of the individual VSDs. Aim 2 will develop a machine learning model to decipher how alterations to the VSD activations change the overall ionic current. Aim 3 will conclude the proposal by looking at changes in the effectiveness of the class 1b anti-arrhythmic drugs lidocaine, mexiletine, and ranolazine in response to varying levels of each subunit. This proposal has implications that stretch both at the biophysical understanding of the Nav1.5 channel to the clinical application in the use of specific anti-arrhythmic drugs. The overall application will provide rigorous and exemplary training for the applicant to successfully become a translation research scientist.