Expression and characterization of Edg‐1 receptors in rat cardiomyocytes

Abstract

Recent evidence indicates that sphingolipids are produced by the heart during hypoxic stress and by blood platelets during thrombus formation. It is therefore possible that sphingolipids may influence heart cell function by interacting with G-protein-coupled receptors of the Edg family. In the present study, it was found that sphingosine 1-phosphate (Sph1P), the prototypical ligand for Edg receptors, produced calcium overload in rat cardiomyocytes. The cDNA for Edg-1 was cloned from rat cardiomyocytes and, when transfected in an antisense orientation, effectively blocked Edg-1 protein expression and reduced the Sph1P-mediated calcium deregulation. Taken together, these results demonstrate that cardiomyocytes express an extracellular lipid-sensitive receptorsystem that can respond to sphingolipid mediators. Because the major source of Sph1P is from blood platelets, we speculate that Edg-mediated Sph1P negative inotropic and cardiotoxic effects may play important roles in acute myocardial ischemia where Sph1P levels are probably elevated in response to thrombus.

Mechanisms of the negative inotropic effects of sphingosine-1-phosphate on adult mouse ventricular myocytes

“…S1P 1 expression levels were almost twofold greater than those of S1P 3 . Other investigators have also reported high levels of S1P 1 in mouse heart (55) and isolated human (20,36) and rat ventricular myocytes (33,39). S1P 3 has also been routinely identified in myocardium of various species (14,33).…”

“…S1P 1 has been detected in abundance in neonatal rat cardiomyocytes (39). In these cells, exposure to S1P (500 nM) results in an initial negative inotropic effect (reduction of systolic calcium).…”

Sphingosine-1-phosphate: distribution, metabolism and role in the regulation of cellular functions

“…Low ceramide concentration treatment of mitochondria isolated from ischemia-exposed SH-SY5Y neuroblastoma cells resulted in reactive oxygen species (ROS)-induced controlled opening of the mPTP that could reduce mitochondrial Ca 2+ overload and explain the sphingolipid protective mechanism. S1P-mediated Ca 2+ overload in rat cardiomyocytes could be reduced by EDG-1 protein expression inhibition with EDG-1 antisense cDNA transfection [69]. S1P is implicated in the maintenance of increased peripheral resistance in heart failure via p38 MAPK-mediated deactivation of myosin light chain phosphatase [70].…”

“…Cellular receptors are a pathway for beneficial or harmful effects of these mediators and a response may depend on receptor subtypes and the signaling pathways it activates in a defined cell [131]. S1P might produce Ca 2+ overload in cardiomyocytes [69]. Blocking of S1P(1)R expression with an antisense approach caused a decrease in S1P-mediated Ca 2+ deregulation, leading to speculation that S1P release by platelets during aggregation and thrombosis, may be involved in acute myocardial ischemia due to S1P's negative inotropic and cardiotoxic effects [69].…”

“…S1P might produce Ca 2+ overload in cardiomyocytes [69]. Blocking of S1P(1)R expression with an antisense approach caused a decrease in S1P-mediated Ca 2+ deregulation, leading to speculation that S1P release by platelets during aggregation and thrombosis, may be involved in acute myocardial ischemia due to S1P's negative inotropic and cardiotoxic effects [69]. Because of its negative inotropic effects, S1P may induce bradycardia in mammalian hearts by means of altering in conductance of cell membrane ion channels resulting in action potential duration shortening in the atrium.…”