Evidence for enhanced M3 muscarinic receptor function and sensitivity to atrial arrhythmia in the RGS2-deficient mouse

Abstract

Atrial fibrillation (AF) is the most common arrhythmia seen in general practice. Muscarinic ACh receptors (M2R, M3R) are involved in vagally induced AF. M2R and M3R activate the heterotrimeric G proteins, G(i) and G(q), respectively, by promoting GTP binding, and these in turn activate distinct K(+) channels. Signaling is terminated by GTP hydrolysis, a process accelerated by regulator of G protein signaling (RGS) proteins. RGS2 is selective for G(q) and thus may regulate atrial M3R signaling. We hypothesized that knockout of RGS2 (RGS2(-/-)) would render the atria more susceptible to electrically induced AF. One-month-old male RGS2(-/-) and C57BL/6 wild-type (WT) mice were instrumented for intracardiac electrophysiology. Atrial effective refractory periods (AERPs) were also determined in the absence and presence of carbachol, atropine, and/or the selective M3R antagonist darifenacin. Susceptibility to electrically induced AF used burst pacing and programmed electrical stimulation with one extrastimulus. Real-time RT-PCR measured atrial and ventricular content of RGS2, RGS4, M2R, M3R, and M4R mRNA. AERP was lower in RGS2(-/-) compared with WT mice in both the high right atrium (HRA) (30 +/- 1 vs. 34 +/- 1 ms, P < 0.05) and mid right atrium (MRA) (21 +/- 1 vs. 24 +/- 1 ms, P < 0.05). Darifenacin eliminated this difference (HRA: 37 +/- 2 vs. 39 +/- 2 ms, and MRA: 30 +/- 2 vs. 30 +/- 1, P > 0.4). RGS2(-/-) were more susceptible than WT mice to atrial tachycardia/fibrillation (AT/F) induction (11/22 vs. 1/25, respectively, P < 0.05). Muscarinic receptor expression did not differ between strains, whereas M2R expression was 70-fold higher than M3R (P < 0.01). These results suggest that RGS2 is an important cholinergic regulator in the atrium and that RGS2(-/-) mice have enhanced susceptibility to AT/F via enhanced M3 muscarinic receptor activity.

Cardiotonic Steroids Stabilize Regulator of G Protein Signaling 2 Protein Levels

“…CTS effects to increase RGS2 expression may influence (Tuomi et al, 2010). We found that digoxin caused RGS2-dependent suppression of M 3 receptor signaling (Fig.…”

Regulators of G-Protein-Signaling Proteins: Negative Modulators of G-Protein-Coupled Receptor Signaling

“…This difference in brain structure resulted in increased anxiety (quantitated by a test for light/darkness preference) and decreased male aggression. Even though no mechanisms were elucidated in how RGS2 might control the various responses in organs, the knockout mice provided a foundation for understanding the physiological functions of RGS2 (Tuomi et al, 2010). Recent genetic quantitative trait analysis has shown that RGS2 is a gene that controls anxiety in mice and possibly humans (Hettema et al, 2013;Le-Niculescu et al, 2011;Lifschytz et al, 2012;Mouri et al, 2010;Muinos-Gimeno et al, 2011;Okimoto et al, 2012;Otowa et al, 2011;Stein et al, 2014;Yalcin et al, 2004).…”

“…Several functional studies have demonstrated the role of RGS4 in the regulation of opioid, cholinergic, and serotonergic receptor signaling in the brain (Fourla et al, 2012;Guasch et al, 2013;Jones et al, 2012;Kong and Tobin, 2011;Leone et al, 2000;Li et al, 2013a;Lifschytz et al, 2012;McOmish et al, 2008;Osterberg et al, 2011;Park et al, 2011;Rivero et al, 2012;Ruiz de Azua et al, 2012a;Stratinaki et al, 2013;Traynor, 2012;Tuomi et al, 2010;Wamsteeker Cusulin et al, 2013;Wang and Traynor, 2011). Upon morphine administration, RGS4 levels rose in the rat LC and decreased immediately after opiate removal.…”

Regulator of G-protein signaling 2 (RGS2) in cardiology and oncology

“…Muscarinic receptors are GPCRs (G protein-coupled receptors), and as such they activate heterotrimeric G proteins by catalyzing GDP dissociation from the Gα subunit and consequently promoting GTP binding [17,18]. Regulator of G-protein signaling 2 (RGS2) is a member of a large family of proteins that all regulate signaling through GPCRs by accelerating GTPase [19-21]-activity on active Gα as well as through other mechanisms.…”

“…Regulator of G-protein signaling 2 (RGS2) is a member of a large family of proteins that all regulate signaling through GPCRs by accelerating GTPase [19-21]-activity on active Gα as well as through other mechanisms. RGS2 has an inhibitory effect on M3-muscarinicacetylcholine receptors (M 3 -mAChRs) [17,22]. M 3 -mAChRs couple to Gαq to activate the G q -phospholipase C (PLC)-protein kinase C (PKC) pathway [23], and the potassium channel I KM3 [23,24].…”