(A). pathway is sufficient to protect the sodium channel from oxidant induced inactivation and suggests the potential use of isoketal scavengers as novel therapeutics to prevent arrhythmogenesis during myocardial infarction. Keywords:ion channels, oxidative stress, reactive carbonyls, arrhythmia == 1. Introduction == The cardiac sodium (Na+) current (INa), contributes to the initiation and morphology of cardiac action potentials as well as to the propagation of electrical impulses, and is thus a key factor for maintaining normal cardiac rhythm. Indeed, dysfunction of Na+channels in various pathophysiological conditions leads to multiple life-threatening arrhythmias. For example, genetic changes inSCN5A, which encodes the pore-forming subunit of the cardiac voltage-gated Na+channel (NaV1.5), cause at least four distinct types of inherited arrhythmia disorders, including the long QT syndrome (LQTS), Brugada syndrome, atrioventricular conduction block, and familial sick AZD3839 free base sinus syndrome [14]. In ischemic myocardium, the normal function of INais compromised. INain surviving myocytes from the epicardial border zone of canine hearts at 5-days post infarct is reduced and considered to be a contributing factor to reentrant ventricular tachyarrhythmias [5,6]. Moreover, following an ischemic event, the modification of INafunction combined with pharmacological blockade of INaenhances the likelihood of life-threatening arrhythmias. As documented in the CAST Study, class Ic anti-arrhythmic drugs (Na+channel blockers) increased the mortality of patients with recent myocardial infarction [7]. Myocardial infarction, with its concomitant ischemia and pressure overload, results in increased production of reactive oxygen species (ROS) [8,9]. In turn, ROS modify cellular lipids, proteins and nucleic acids. Ischemia/reperfusion induces ventricular tachyarrhythmias in isolated perfused hearts that can be blocked by cocktails of antioxidant enzymes and small molecular weight antioxidants [10,11]. In isolated myocytes, the oxidant tert-butylhydroperoxide (t-BHP) or photoinduced oxidizers dramatically reduce INa[1214]. Oxidants induce a wide range of modifications to cellular lipids, nuclei acids, and protein, so that a large number of potential mechanisms could NES mediate the impact of ROS upon INain ischemic hearts. One potential mediator of these effects are AZD3839 free base reactive lipoxidation products that modify the sodium channel, as addition of reactive lipoxidation products induce changes in INa[14,15]. However, whether reactive lipoxidation products alters INadirectly via adduction to NaV1. 5 or indirectly by adduction to other targets is unknown; to date, there has been no direct evidence that NaV1.5 is modified by lipoxidation products under oxidative conditions or that specifically blocking lipoxidative modification prevents the changes in INa. One recent advance that facilitates the identification of lipid modified proteins in cultured cells has been the use of click chemistry to form a AZD3839 free base stable triazole linkage between a terminal alkyne on the lipid of interest and a biotin-linked azide that is added during the final stages of the experiments [1622]. Modification of fatty acids with a terminal alkyne (alkynyl-fatty acids) does not significantly alter the physical properties of the fatty acid, so that alkynyl fatty acids are readily incorporated into membrane phospholipids and serve as substrate for enzymes in a manner virtually identical to unmodified fatty acids [23]. Therefore, peroxidation of alkynyl polyunsaturated fatty acids in cellular membranes likely forms reactive lipid aldehydes that retain the terminal alkyne (Fig. 1A, line 3). Proteins that are adducted by these lipid aldehydes can then be captured by ex vivo reaction of this alkyne with biotin-azide followed by streptavidin-based affinity purification [16] (Fig. 1A, last line). == Fig. 1. == (A) Schematic outline depicting the identification of proteins modified by peroxidation products of arachidonic acid in cells treated with ROS initiators. Arachidonic acid modified to have a terminal alkyne (al-AA) is incubated with cells to allow its incorporation into membrane phospholipids. Cells are then treated with ROS initiators (iron/adenosine/ascorbate ort-BHP) which peroxidize polyunsaturated fatty acids including al-AA to generate lipoxidation products (including al-IsoK.) The al-IsoK then reacts rapidly with cellular proteins, potentially including NaV1.5. After the end of the treatment period, adducted proteins are captured from cellular lysates using click chemistry. In the presence of copper catalyst, biotin-linked azide (biotin-N3) selectively reacts with terminal alkynes to form a triazole linkage between the adducted protein and the biotin. Adducted proteins can then be captured on streptavidin beads, the captured proteins run on SDS-PAGE and immunoblotted for candidate proteins including NaV1.5. (B) Exposure of HEK NaV1.5-GFP cells to oxidants results in channel modification by arachidonic.