Role of Endothelin-1 in Right Atrial Arrhythmogenesis in Rabbits with Monocrotaline-Induced Pulmonary Arterial Hypertension

Abstract

Atrial arrhythmias are considered prominent phenomena in pulmonary arterial hypertension (PAH) resulting from atrial electrical and structural remodeling. Endothelin (ET)-1 levels correlate with PAH severity and are associated with atrial remodeling and arrhythmia. In this study, hemodynamic measurement, western blot analysis, and histopathology were performed in the control and monocrotaline (MCT, 60 mg/kg)-induced PAH rabbits. Conventional microelectrodes were used to simultaneously record the electrical activity in the isolated sinoatrial node (SAN) and right atrium (RA) tissue preparations before and after ET-1 (10 nM) or BQ-485 (an ET-A receptor antagonist, 100 nM) perfusion. MCT-treated rabbits showed an increased relative wall thickness in the pulmonary arterioles, mean cell width, cross-sectional area of RV myocytes, and higher right ventricular systolic pressure, which were deemed to have PAH. Compared to the control, the spontaneous beating rate of SAN-RA preparations was faster in the MCT-induced PAH group, which can be slowed down by ET-1. MCT-induced PAH rabbits had a higher incidence of sinoatrial conduction blocks, and ET-1 can induce atrial premature beats or short runs of intra-atrial reentrant tachycardia. BQ 485 administration can mitigate ET-1-induced RA arrhythmogenesis in MCT-induced PAH. The RA specimens from MCT-induced PAH rabbits had a smaller connexin 43 and larger ROCK1 and phosphorylated Akt than the control, and similar PKG and Akt to the control. In conclusion, ET-1 acts as a trigger factor to interact with the arrhythmogenic substrate to initiate and maintain atrial arrhythmias in PAH. ET-1/ET-A receptor/ROCK signaling may be a target for therapeutic interventions to treat PAH-induced atrial arrhythmias.

Keywords: Endothelin-1; atrial arrhythmogenesis; pulmonary arterial hypertension.

Figure 1

Representative pulmonary vascular, alveoli, and right ventricular (RV) histological features, and RV systolic pressure (RVSP) in the control and the monocrotaline (MCT)-treated hearts. (A) Hematoxylin and eosin (H&E) staining of pulmonary arterioles (original magnification × 10) and relative wall thickness of pulmonary arterioles from the control (n = 27 cells) and the MCT-treated (n = 33 cells) groups. Relative wall thickness was calculated as [2 × wall thickness/external diameter] × 100%. (B) Representative hematoxylin and eosin (H&E) staining of the RV (original magnification × 40) as well as cell width and cross-sectional area of RV myocytes from the control (n = 21 cells) and the MCT-treated (n = 21 cells) groups. (C) Representative tracings and average data of the RVSP in the control (N = 4) and the MCT-treated (N = 5) rabbits.

Figure 2

Action potential (AP) characteristics of the right atrial (RA) tissue preparations from control or monocrotaline (MCT)-treated hearts with or without endothelin (ET)-1 treatment. (A) Examples and average data of the APs of RA preparations from MCT-induced PAH rabbits (N = 10) and control rabbits (N = 10). (B) Examples and average data of the APs of RA preparations from MCT-induced PAH rabbits (N = 6) treated with or without ET-1 (10 nM). AP durations at 20%, 50%, and 90% repolarization of the AP amplitude (APD₂₀, APD₅₀, and APD₉₀) were measured at 2 Hz; AP amplitude, APA; RMP, resting membrane potential.

Figure 3

The spontaneous activity of sinoatrial node-right atrium (SAN–RA) preparations from control or monocrotaline (MCT)-treated rabbits and the effect of endothelin (ET)-1 on the spontaneous activity of sinoatrial node (SAN)–right atrium (RA) preparations from the control or monocrotaline (MCT)-treated rabbits. Representative tracings and average data of the AP morphology in SAN–RA preparations with or without ET-1 (10 nM) from the control (left panel, N = 7) or MCT-treated (right panel, N = 9) rabbits are shown.

Figure 4

Conduction block and premature atrial beats with retrograde conduction in the sinoatrial node (SAN)–right atrium (RA) preparations from monocrotaline (MCT)-treated rabbits recorded by the conventional glass electrode. (A) Representative recordings of the conduction block from the SAN to the RA presented with a 6:1 conduction block (upper panel) or a long pause (lower panel). (B) Representative recordings of premature atrial beats with retrograde conduction from the RA to the SAN.

Figure 5

The electrical activities of endothelin (ET)-1-treated sinoatrial node (SAN)–right atrium (RA) preparations from monocrotaline (MCT)-treated rabbits were recorded by the conventional glass electrode. (A) A representative recording of short runs of atrial tachycardia (indicated by a black asterisk on top) in ET-1-treated SAN–RA preparations from MCT-treated rabbits. (B) Representative recordings revealed reentry as a mechanism of initiation of ET-1-induced short runs of atrial tachycardia in MCT-treated SAN–RA preparations.

Figure 6

Effects of BQ 485 (an endothelin-A receptor antagonist) on the electrical activity of endothelin (ET)-1-treated sinoatrial node–right atrium (SAN–RA) preparations from monocrotaline (MCT)-treated rabbits. The representative tracings demonstrate the electrical activity of MCT-treated SAN–RA preparations after ET-1 (10 nM) and BQ 485 (100 nM) administration.

Figure 7

Western blot analysis of connexin 43, protein kinase G (PKG), RhoA/Rho kinase 1 (ROCK1), Akt and phosphorylated Akt (p-Akt) of right atrium (RA) tissue from control rabbits or rabbits with monocrotaline (MCT)-induced pulmonary arterial hypertension (PAH). Representative images and the relative expression of connexin 43 (N = 12), PKG (N = 8), ROCK1 (N = 7), Akt (N = 8), p-Akt (N = 7) in the control and MCT-induced PAH groups. Data are presented as the mean ± standard error of the mean.