Effect of sphingosine on Ca2+ entry and mitochondrial potential of Jurkat T cells -: Interaction with Bcl2

Triggers of Jurkat T cell apoptosis include sphingosine and ceramide. Sphingosine and ceramide further inhibit capacitative Ca2+ entry (I-CRAC), an effect leading to inactivation but not death of Jurkat T cells. Mitochondria are key organelles in the machinery leading to apoptosis and on the other hand have been shown to participate in the regulation of Ca2+ entry. The present experiments were performed to explore whether treatment of Jurkat T cells with sphingosine leads to apoptosis and reduced Ca2+ entry and whether those effects are sensitive to expression of the antiapoptotic protein Bcl(2), localized in the outer mitochondrial membranes Exposure of Jurkat T cells to 10 mu M spingosine was according to DiOC(6) fluorescence followed by mitochondrial depolarization and according to Fura-red/Fluo-3 fluorescence followed by decreased capacitative Ca2+ entry. Mitochondrial depolarization was significantly delayed in cells overexpressing wild type BCl2 or Bcl(2) targeted to the mitochondrial membrane, whereas no significant influence on mitochondrial depolarization was observed in cells expressing Bcl(2) lacking the membrane targeting motif or Bcl(2) targeted to the encloplasmatic reticulum. In contrast to mitochondrial potential, the blunting of capacitative Ca2+ entry following sphingosine treatment was not sensitive to mitochondrial Bcl(2) expression. In conclusion sphingosine exposure leads to both, mitochondrial depolarization and inhibition of capacitative Ca2+ entry. Mitochondrial Bcl(2) reverses the effect on mitochondria but not on Ca2+ entry and thus leads to dissociation of those two sequelae of sphingosine treatment. Copyright (C) 2005 S. Karger AG, Basel.