Abstract 17032: Substrate Stiffness Alters the Kinetics of Sodium Channel Nav1.5 and Depolarization of Cardiomyocytes

Abstract

Background: Myocardial scarring after infarction (MI) can create areas of slowed conduction, which can lead to re-excitation of the heart, or re-entry. Reentrant arrhythmia is one of the electrophysiological mechanisms responsible for ventricular tachycardia after acute myocardial infarction (AMI). Since the sodium channel (Na v 1.5) is a major contributor to cardiac electrical conduction, the objective of this study was to evaluate the effect of cell substrate stiffness on the kinetics of the Na v 1.5. Methods: MI was created by permanent ligation of the left anterior descending artery in rats. After 7 days, hearts were decellularized and grossed into 1 mm rings for measuring stiffness by using an atomic force microscope. The hearts had an elastic modulus of 263.33±76.8 kPa at scar, and 27.26±3.97 kPa at a remote area (n=3). The surface of p olydimethylsiloxane (PDMS) gels was tuned to match the stiffness of decellularized infarcted rat hearts (17.04±2.02 kPa, 110.56±8.70 kPa and 328.4±45.72 kPa, respectively, n=3). Human embryonic kidney 293 (HEK-293) cells were induced to stably express human Na v 1.5. HEK-293 and human pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) were separately cultured on the PDMS substrate that mimicked stiffness of infarcted rat hearts for 24 h. Sodium channel currents (I Na ) and action potentials (APs) were recorded by patch clamp techniques. Results: As substrate stiffness increased, HEK-293 voltage dependent activation of Na v 1.5 (I Na ) shifted significantly towards more positive voltage (Vhalf: -28.42±5.12 mV, -33.47±6.98 mV, -19.84±5.24 mV, respectively, p<0.01 in one-way ANOVA, n=12), and the transition from closed-state into inactivation was faster (tau: 48.47±4.60ms, 40.67±8.07ms, 81.20±9.54ms, p<0.05, n=12). However, the current density, the steady-state inactivation curve and the recovery time were comparable between different PDMS. In iPSC-CMs, the slope of AP upstroke was decreased when stiffness was increased (30.00±1.38V/s, 23.91±0.65V/s, 20.93±0.34V/s, p<0.05, n=15). Conclusion: Increased substrate stiffness, similar to myocardial scar, alters the kinetics of Na v 1.5 and affects the depolarization of cardiomyocytes, which likely contributes to slow conduction after MI.