TY - JOUR T1 - Guanine Nucleotide-Sensitive Inhibition of L-Type Ca<sup>2+</sup> Current by Lysosphingolipids in RINm5F Insulinoma Cells JF - Molecular Pharmacology JO - Mol Pharmacol SP - 862 LP - 869 VL - 53 IS - 5 AU - Herbert M. Himmel AU - Dagmar Meyer zu Heringdorf AU - Bernd Windorfer AU - Chris J. van Koppen AU - Ursula Ravens AU - Karl H. Jakobs Y1 - 1998/05/01 UR - http://molpharm.aspetjournals.org/content/53/5/862.abstract N2 - The lysosphingolipids sphingosine-1-phosphate (SPP) and sphingosylphosphorylcholine (SPPC) reportedly increase free cytosolic Ca2+ concentration ([Ca2+]i) in a variety of cell types, apparently by activating G protein-coupled plasma membrane receptors. We investigated whether and how sphingolipids modulate Ca2+ homeostasis in the insulinoma cell line RINm5F. The addition of SPPC and glucopsychosine (GPS) did not affect basal [Ca2+]i but inhibited the KCl (30 mm)-induced increase in [Ca2+]i in a pertussis toxin-insensitive and concentration-dependent manner (EC50 ∼ 5 μm). Similar inhibitory effects were observed with dihydro-SPPC and psychosine, whereas SPP and variousN-acylated sphingolipids (at 10 μm each) had little or no effect on the KCl-induced [Ca2+]i increase. Because in RINm5F cells the primary pathway for depolarization-induced [Ca2+]i increase are L-type Ca2+ channels, we studied whether sphingolipids reduceL-type Ca2+ current (ICa.L). When added to the bath, GPS and SPPC, but not SPP (10 μmeach), rapidly reduced maximal ICa.L by ∼35%, similar to the α2-adrenoceptor agonist clonidine (30 μm). However, when applied internally, GPS had no effect on ICa.L. When the electrode solution contained the stable GDP analog guanosine-5′-O-(2-thio)diphosphate (1 and 10 mm), the inhibitory effect of GPS was abolished. In conclusion, a novel cellular action of lysosphingolipids is observed in RINm5F cells (i.e., a guanine nucleotide-sensitive inhibition ofL-type Ca2+ currents). The pharmacological profile of this inhibition is unique and unlike any known lysosphingolipid receptor-mediated action. The American Society for Pharmacology and Experimental Therapeutics ER -