TY - JOUR T1 - Bitopic S1P<sub>3</sub> Antagonist Rescue from Complete Heart Block: Pharmacological and Genetic Evidence for Direct S1P<sub>3</sub> Regulation of Mouse Cardiac Conduction JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.115.100222 SP - mol.115.100222 AU - M.Germana Sanna AU - Kevin P Vincent AU - Emanuela Repetto AU - Nguyen Nhan AU - Steven J Brown AU - Lusine Abgaryan AU - Sean W Riley AU - Nora B Leaf AU - Stuart M Cahalan AU - William B Kiosses AU - Yasushi Kohno AU - Joan Heller Brown AU - Andrew D McCulloch AU - Hugh Rosen AU - Pedro J Gonzalez-Cabrera Y1 - 2015/01/01 UR - http://molpharm.aspetjournals.org/content/early/2015/10/22/mol.115.100222.abstract N2 - The molecular pharmacology of the G-protein coupled receptors for Sphingosine 1-Phosphate (S1P) provides important insight into established and new therapeutic targets. A new, potent bitopic S1P3 antagonist, SPM-354, with in vivo activity has been used, together with S1P3-knockin and -knockout mice to define spatial and functional properties of S1P3 in regulating cardiac conduction. We show that S1P3 is a key direct regulator of cardiac rhythm both in vivo and in isolated perfused hearts. FTY720 (2-amino-2-[2-(4-octylphenyl)ethyl]propane-1,3-diol) in vivo, and S1P in isolated hearts, induced a spectrum of cardiac effects ranging from sinus bradycardia to complete heart block, as measured by surface ECG in anesthetized mice, and in volume-conducted Langendorff preparations. Agonist effects on complete heart block are absent in S1P3-knockout mice, and are reversed, in wild type mice, with SPM-354, characterized and described here. Homologous knockin of S1P3-mCherry is fully functional pharmacologically, and is strongly expressed, by IHC confocal microscopy, in HCN4-positive atrioventricular node and His-Purkinje fibers, with relative less expression in HCN4-positive sinoatrial node. In Langendorff studies, at constant pressure, SPM-354 restored sinus rhythm in S1P-induced complete heart block, and fully reversed S1P mediated bradycardia. S1P3 distribution and function in the mouse ventricular cardiac conduction system suggest a direct mechanism for heart block risk that should be further studied in humans. A richer understanding of receptor and ligand usage in the pacemaker cells of the cardiac system is likely to be useful in understanding ventricular conduction in health, disease and pharmacology. ER -