Sphingosine Inhibits Voltage-operated Calcium Channels in GH4C1 Cells

In the present study we investigated the mechanism of inhibitory action of sphingosine (SP) on voltage-activated calcium channels (VOCCs) in pituitary GH4C1 cells. Using the patch-clamp technique in the whole-cell mode, we show that SP inhibits Ba2+ currents (IBa) when 0.1 mm BAPTA is included in th...

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Veröffentlicht in:The Journal of biological chemistry 1998-01, Vol.273 (1), p.242-247
Hauptverfasser: Titievsky, Alexey, Titievskaya, Ira, Pasternack, Michael, Kaila, Kai, Törnquist, Kid
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Sprache:eng
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Zusammenfassung:In the present study we investigated the mechanism of inhibitory action of sphingosine (SP) on voltage-activated calcium channels (VOCCs) in pituitary GH4C1 cells. Using the patch-clamp technique in the whole-cell mode, we show that SP inhibits Ba2+ currents (IBa) when 0.1 mm BAPTA is included in the patch pipette. However, when the BAPTA concentration was raised to 1–10 mm, SP was without a significant effect. The effect of SP was apparently not mediated via a kinase, as it was not inhibited by staurosporine. By using the double-pulse protocol (to release possible functional inhibition of the VOCCs by G proteins), we observed that G proteins apparently evoked very little functional inhibition of the VOCCs. Furthermore, including GDPβS (guanyl-5′-yl thiophosphate) in the patch pipette did not alter the inhibitory effect of SP on the Ba2+ current, suggesting that SP did not modulate the VOCCs via a G protein-dependent pathway. Single-channel experiments with SP in the pipette, and experiments with excised outside-out patches, suggested that SP directly inhibited VOCCs. The main mechanism of action was a dose-dependent prolongation of the closed time of the channels. The results thus show that SP is a potent inhibitor of VOCCs in GH4C1 cells, and that calcium may be a cofactor in this inhibition.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.273.1.242