Expression of sphingosine‐1‐phosphate receptors in neonatal and adult mouse heart

Abstract

Sphingosine-1-phosphate (S1P) is a cell membrane-associated sphingolipid secreted into serum/plasma by activated platelets and mast cells.S1P can affect cellular proliferation/survival, motility, and [Ca++]i regulation, as well as heart rate and arterial tone. S1P binds with high affinity to 5 distinct GPCR, also known as endothelial differentiation gene (EDG) receptors: S1P1/EDG1, S1P2/EDG5, S1P3/EDG3, S1P4/EDG6, and S1P5/EDG8. Since S1P is known to affect ionic currents in ventricular, atrial, and sino-atrial node myocytes, the objective of this study was to characterize S1P receptor expression levels in these neonatal and adult mouse cardiac tissues. Hearts were washed thoroughly in Ca++-free Tyrodes buffer, defined chambers were dissected, and total RNA was extracted and reverse transcribed. Quantitative RT-PCR was performed using specific primer sets for S1P1–3.S1P1 expression in neonatal right atria (RA) was significantly greater (p<0.05) than in the left (LV) or right ventricles (RV). S1P1 expression in adult RA was also significantly greater (p<0.05) than LV or RV.S1P3 expression was detected only in neonatal mouse RV (vs. LA, p<0.05), and S1P2 expression was measured significant only for adult RA (vs. LV, p<0.05). In summary, neonatal cardiac tissues had larger expression levels than adult tissues for S1P1.S1P2–3 showed fewer differences, perhaps due to lower expression levels and higher variability. The relatively high expression of S1P receptors in RA may partially explain the pronounced negative chronotropic effect of S1P on heart rate and its ability to shorten atrial action potential duration. Supported in part by a NSF Fellowship and an AHA grant.