Abstract 19257: TRPC3 and IP3 Regulate Angiotensin II Induced Ca2+ Dependent Arrhythmias in Mouse and Human Cardiomyocytes
Angiotensin II (ATII) is associated with cardiac remodeling, heart failure and arrhythmia. In cardiomyocytes (CM), ATII signals primarily via the Gq-coupled ATII receptor type 1 (AT1), phospholipase C signaling pathway including IP3-mediated Ca release and diacylglycerol activation of protein kinase C. Diastolic Ca release from the sarcomplasmic reticulum (SR) triggers arrhythmogenic inward current via the sarcolemmal Na-Ca-exchanger (NCX). Recent evidence suggests that TRPC3 channels and NCX may also be regulated by ATII contributing to arrhythmogenity. We investigated the mechanisms of Ca-mediated cellular arrhythmias induced by ATII. In CM from murine or human non-failing left ventricle, [Ca] transients (Fluo4-AM) during 1 Hz, as well as SR Ca load (caffeine), SR Ca leak (Ca spark frequency,SparkF) and arrhythmic (arrh) action potentials (as synchronized diastolic Ca release) during prolonged diastole were quantified in confocal images. Action potentials (AP) were recorded (current clamp) in a subset of cells. ATII (100 nM,20 min) in combination with IP3-inhibitor 2-ABP (3 µM) or TRPC3-inhibitor Pyr3 (10 µM), or ouabain (100 nM) were used in parallel experiments. In mouse CM ATII increased [Ca] transient amplitude (F/F0: 4.1±0.3 vs. 2.7±0.2 in CTRL). ATII also induced Ca sparks (SparkF (s-1*pL-1): 277±28 vs. 48±20) and arrhAP (0.77±0.12 vs. 0.03±0.01arrhAP*s-1) despite unchanged SR [Ca]. ATII induced significantly more arrhAP than ouabain (0.06±0.02) despite similarly increased SparkF (ouabain: 284±44). ATII tended to increase AP duration from 53±6 to 92±34 ms (APD90; P=0.1). 2-APB significantly reduced ATII -induced Ca sparks and arrhAP. In CM matched for SR Ca leak (SparkF), 2-APB significantly reduced - and Pyr3 abolished ATII-induced arrhAP. ATII was also arrhythmogenic in human non-failing CM (SparkF: 407±93 vs. 90±23 in CTRL;cells with arrhAP: 6/10 vs. 2/11; p<0.05). Pyr3 also effectively reduced AT-II induced arrhythmogenity in human CM (SparkF: 101±21; 0/7 cells with arrhAP; both P<0.05).
Conclusion: ATII facilitates Ca-dependent arrhythmias by mechanisms beyond an increase in SR Ca leak in mouse and human CM. TRPC3-channels promote the arrhythmogenity of diastolic SR Ca release in the presence of ATII.
- © 2012 by American Heart Association, Inc.