Electrophysiological Comparison of NaV1.5 Expressed in HEK293 Cells to Native NaV Currents in Cardiac Myocytes
Valinsky, William Corey
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Contraction of cardiac muscle is a highly regulated event that relies on a delicate balance of ions entering and leaving the cell through ion channels. In particular, voltage gated sodium channels are responsible for the rapid depolarization that leads to a contraction. During an oxidative challenge, sodium channels rapidly activate, but do not fully turn off. This alters the rate of cardiac repolarization and can induce cardiac arrhythmias. It is currently unknown whether the most common sodium channel isoform found in the heart, NaV1.5, generates this oxidant-induced persistent current or if other isoforms are responsible. Therefore, I sought to further explore the biophysical properties NaV1.5, and determine if it can enter this persistent mode. I tested the biophysical properties of native INa in cardiac myocytes and in NaV1.5 transfected HEK293 cells under macro cell-attached voltage-clamp. I used a sodium channel enhancer (Anemonia sulcata toxin II; 10 nM), a sodium channel blocker (tetrodotoxin; 10 nM) and a model of oxidative stress (H2O2; 100 µM, 200 µM, 1000 µM) to compare and contrast the cellular responses between both cell types. I observed that transfected HEK293 cells and cardiac myocytes were unaffected by H2O2 at various concentrations. Given the lack of other isoforms in transfected HEK293 cells, and the low abundance (<5%) of other isoforms in cardiac myocytes, I propose that NaV1.5 function is unaffected by H2O2. Furthermore, ATX II prolonged the inactivation process in both HEK293 cells and cardiac myocytes in a voltage-dependent manner, indicating that NaV1.5 can give rise to persistent sodium current. Finally, by comparing both cell types under control settings, I found that transfected HEK293 cells inactivated at a much slower rate and at more negative potentials compared to the current in cardiac myocytes. My results suggest that NaV1.5 does not underlie oxidant-induced persistent current and that β subunits likely play a significant role in the inactivation process.