TRPC3 Channels in Angiotensin II-Induced Calcium- Dependent Arrhythmias in Mouse and Human Cardiomyocytes

Abstract

Angiotensin II (ATII) is associated with cardiac remodeling, heart failure and arrhythmias. In cardiomyocytes (CM), ATII signaling involves IP3- and DAG-dependent pathways and results in increased diastolic Ca release from the sarcoplasmic reticulum (SR). 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 action potentials (arrAP, as non-stimulated synchronized Ca release) were visualized confocally. Action potentials (AP) were recorded in a subset of cells. ATII (100 nM,20 min), IP3-inhibitor 2-ABP, TRPC3-inhibitor Pyr3, or Na/K-pump inhibitor ouabain (100 nM) were used in parallel experiments. In mouse CM ATII increased the [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±0.01 p<0.05) despite unchanged SR [Ca]. Interestingly, ATII induced significantly more arrhAP than ouabain at comparable SparkF. ATII increased 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 SparkF, ATII-induced arrAP were significantly reduced with Pyr3.ATII induced redistribution of TRPC3 to the sarcolemmal membrane. In human non-failing CM, Pyr3 also reduced ATII-induced arrhythmogeneity.Conclusion: ATII facilitates Ca-dependent arrhythmias by mechanisms beyond an increase in SR Ca leak in mouse and human CM. Sarcolemmal TRPC3-channels may modulate the arrhythmogenity of diastolic SR Ca release in the presence of ATII.