Endothelin-1 promotes cellular electrophysiological remodeling by affecting IKr expression in cardiac HL-1 cells.

The endothelin system is activated in heart failure, a syndrome frequently associated with ventricular arrhythmias. Structural (e.g. hypertrophy) and electrophysiological (e.g. action potential prolongation) remodeling of cardiomyocytes contribute to arrhythmogenesis in heart failure. Endothelin-1 (ET-1) is a potent promoter of myocardial hypertrophy but its effect on cellular electrophysiological remodeling is unknown. Thus, we investigated the electrophysiological properties of a stable murine cardiomyocytic cell line, HL-1, chronically (10-15 days) exposed to ET-1 (100 nM). ET-1 significantly increased cell area (an index of cell hypertrophy) (2817±347 µm2) with respect to controls (CTR, 1995±145 µm2; p<0.05). In patch-clamped HL-1, action potential duration (APD) recorded in ET-1 was significantly prolonged (174.9±25.7 ms, n=12) versus CTR cells (102.7±14.1 ms, n=18) (p<0.001). To investigate the ionic mechanism for APD prolongation, we measured the rapid delayed rectifier K+ current (IKr), which controls the repolarization phase in HL-1. Tail maximal density of IKr was significantly reduced from 10.3±0.1 pA/pF in CTR (n=9) to 4.2±0.1 pA/pF in ET-1 cells (n=14, p<0.001). Midpoint activation was significantly shifted from -6.3±0.3 mV in CTR (n=9) to 1.6±0.9 (n=14, p<0.001) in ET-1 cells. IKr kinetics was significantly slowed down from 21.4±1.2 ms in CTR (n=4) to 86.1±5.5 ms in ET-1 cells (n=7, p<0.001). To get insight into the molecular basis of ET-1-induced chances of IKr properties, mRNA levels of alpha subunit, ERG, and regulatory beta subunits, MiRP-1 (which decreases IKr and slows down activation rate) and minK (which increases IKr and activation rate), were measured by Real Time PCR. Exposure to ET-1 caused a decrease of ERG and minK mRNA compared to CTR cells (0.52±0.05 vs. 1±0.01; 0.513±0.08 vs. 1±0.04; p<0.05); MiRP-1 was not affected. In conclusion, chronic exposure to ET-1 increases cell size and prolongs APD of HL-1 cells; the latter effect is associated with a decrease in IKr density, likely due to a down-regulation in the expression of ERG and minK subunits. Thus, ET-1 acts directly on cardiac myocytes modulating their functional and molecular properties and possibly leading to arrhythmogenic alterations.