Abstract
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.
Footnotes
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Send reprint requests to: Dr. Karl H. Jakobs, Institut für Pharmakologie, Universitätsklinikum Essen, Hufelandstrasse 55, D-45122 Essen, Germany.
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This work was supported by Grant 0310493A from Bayer AG and the Bundesministerium für Bildung and Wissenschaft, Forschung und Technologie and the Juterne Forschungsförderung Essen program of the Universitätsklinikum Essen.
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Preliminary results have been published in abstract form: Himmel HM, Meyer zu Heringdorf D, Windorfer B, van Koppen CJ, Ravens U, and Jakobs KH (1997) Sphingolipid receptor-mediated inhibition ofL-type Ca2+ current in the insulinoma cell line RINm5F. Naunyn-Schmiedebergs Arch Pharmacol355:R52.
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H.M.H. and D.M.z.H. contributed equally to this work.
- Abbreviations:
- SPP
- sphingosine-1-phosphate
- [Ca2+]i
- cytosolic free Ca2+concentration
- GDPβS
- guanosine-5′-O-(2-thio)diphosphate
- GPS
- glucopsychosine
- GTPγS
- guanosine-5′-O-(3-thio)triphosphate
- HEK
- human embryonic kidney
- HEPES
- 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid
- ICa.L
- L-type Ca2+ current
- PKC
- protein kinase C
- PS
- psychosine
- PTX
- pertussis toxin
- SPPC
- sphingosylphosphorylcholine
- EGTA
- ethylene glycol bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid
- Received April 30, 1997.
- Accepted January 21, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
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