Bile Acid-Induced Arrhythmia Is Mediated by Muscarinic M2 Receptors in Neonatal Rat Cardiomyocytes

Abstract

BackgroundIntrahepatic cholestasis of pregnancy (ICP) is a common disease affecting up to 5% of pregnancies and which can cause fetal arrhythmia and sudden intrauterine death. We previously demonstrated that bile acid taurocholate (TC), which is raised in the bloodstream of ICP, can acutely alter the rate and rhythm of contraction and induce abnormal calcium destabilization in cultured neonatal rat cardiomyocytes (NRCM). Apart from their hepatic functions bile acids are ubiquitous signalling molecules with diverse systemic effects mediated by either the nuclear receptor FXR or by a recently discovered G-protein coupled receptor TGR5. We aim to investigate the mechanism of bile-acid induced arrhythmogenic effects in an in-vitro model of the fetal heart.Methods and ResultsLevels of bile acid transporters and nuclear receptor FXR were studied by quantitative real time PCR, western blot and immunostaining, which showed low levels of expression. We did not observe functional involvement of the canonical receptors FXR and TGR5. Instead, we found that TC binds to the muscarinic M2 receptor in NRCM and serves as a partial agonist of this receptor in terms of inhibitory effect on intracellular cAMP and negative chronotropic response. Pharmacological inhibition and siRNA-knockdown of the M2 receptor completely abolished the negative effect of TC on contraction, calcium transient amplitude and synchronisation in NRCM clusters.ConclusionWe conclude that in NRCM the TC-induced arrhythmia is mediated by the partial agonism at the M2 receptor. This mechanism might serve as a promising new therapeutic target for fetal arrhythmia.

The protective effect of ursodeoxycholic acid in an in vitro model of the human fetal heart occurs via targeting cardiac fibroblasts

“…In addition, the concentrations were significantly reduced compared to previously published work (Gorelik et al, 2002;Miragoli et al, 2011a;Sheikh Abdul Kadir et al, 2010;Williamson et al, 2001). …”

G Protein–Coupled Bile Acid Receptor 1 Stimulation Mediates Arterial Vasodilation through a KCa1.1 (BKCa)–Dependent Mechanism

“…In brief, BAs have the capacity to signal via nuclear and G protein-coupled receptors, including G protein-coupled bile acid receptor 1 (GPBAR1), as well as, large conductance Ca 21 activated potassium channel K Ca 1.1 (BK Ca ) (Dopico et al, 2002) and muscarinic receptors (Sheikh Abdul Kadir et al, 2010) in which myriad effects on cardiovascular function have been demonstrated, including changes in myocyte contraction and synchronization (Bogin et al, 1983;Gorelik et al, 2002;Sheikh Abdul Kadir et al, 2010), vasodilation in a number of ex vivo isolated vascular models (Pak and Lee, 1993;Pak et al, 1994;Dopico et al, 2002;Bukiya et al, 2007;Sheikh Abdul Kadir et al, 2010), and bradycardia in vivo (Joubert, 1978a,b). In addition, BA dx.doi.org/10.1124/jpet.113.210005. s This article has supplemental material available at jpet.aspetjournals.org.…”

Intestinal transport and metabolism of bile acids

“…However, bile acids also act through other receptors including muscarinic receptors, the sphingosine-1-phosphate receptor 2, ␣ 5, ␤ 1-integrin, through signal transduction pathways such as those mediated by Jun Nterminal kinase (JNK), ERK, and Akt ( 3,(6)(7)(8), and through posttranslational interactions with proteins ( 9 ). Signaling via these diverse pathways is regulated in part by the local concentration and chemical structure of the bile acid species, which in turn is controlled by hepatic synthesis, host and microbial metabolism, and the enterohepatic circulation.…”