Abstract 13709: TRPV4 Enhances Ca 2+ Transients and Promotes Arrhythmic Ca 2+ Signaling Following Hypoosmotic Stress and Ischemia-Reperfusion

Abstract

Introduction: Transient Receptor Potential Vanilloid 4 (TRPV4) is an osmotically activated Ca 2+ channel which enhances cardiomyocyte Ca 2+ cycling and may contribute to arrhythmic Ca 2+ signals in hypoosmotic stress and Ischemia-Reperfusion (I/R). Hypothesis: TRPV4 overexpression enhances Ca 2+ transient (CaT) amplitude and arrhythmic Ca 2+ events in left ventricular (LV) cardiomyocytes exposed to hypoosmotic stress and Langendorff hearts following I/R. Methods: Mouse LV cardiomyocytes from TRPV4 Overexpressors (OEX) and non-transgenic controls (CTL) were exposed to hypoosmotic stress (250 mOsm, 30min). CaT amplitude (paced 0.5 Hz) and arrhythmic Ca 2+ events (prolonged kinetics, spontaneous CaT, Ca 2+ waves) were monitored via confocal imaging (fluo-4, 100Hz). I/R (45min global ischemia, 30min reperfusion) experiments were conducted in OEX and CTL Langendorff hearts expressing the GCaMP6f Ca 2+ sensor (OEX-GCaMP, CTL-GCaMP). CaT and arrhythmic Ca 2+ signals (Ca 2+ waves, alternans, Ca 2+ overload) were monitored in the LV myocardium. Experiments were conducted in the absence and presence of TRPV4 inhibition by HC067047 (HC, 1uM). Results: Incidence of arrhythmic Ca 2+ signals during minutes 0-15 of hypoosmotic stress was increased in OEX cardiomyocytes vs CTL (78 vs 20%, P<0.05, N=9, 5) and prevented in OEX by HC (11%, P<0.05, N=9). Arrhythmia score was increased in OEX vs CTL (1.3±0.7 vs. 0.1±0.1, P<0.05, N=9, 5) and decreased in OEX by HC (0.2±0.2, P<0.05, N=9). Following hypoosmotic stress, CaT amplitude was elevated in OEX vs CTL (F/F 0 = 3.6±0.4 vs 2.1±0.4, P<0.05, N=7, 4) and this effect in OEX was prevented by HC (F/F 0 =2.4±0.4, P<0.05, N=8). Langendorff OEX-GCaMP hearts subjected to I/R demonstrated increased systolic Ca 2+ (F/F 0 =1.8±0.09 vs 1.3±0.1, P<0.05, N=5, 6) during minutes 10-30 of reperfusion, which was attenuated by HC (F/F 0 =1.4±0.08, P<0.05, N=4). OEX-GCaMP hearts were more likely to demonstrate arrhythmic Ca 2+ signals during minutes 15-30 of reperfusion than CTL-GCaMP (27/487 vs 0/415 cells, p<0.05 N=5, 6) and this effect in OEX-GCaMP was prevented by HC (0/633 cells, p<0.05, N=4). Conclusions: TRPV4 activation enhances Ca 2+ transients and promotes arrhythmic Ca 2+ signals, and may provide a novel anti-arrhythmic target in I/R.