Sphingosine inhibition and promotion of histamine release from isolated rat mast cells.

Sphingosine inhibited the histamine release induced by antigen, compound 48/80 with and without calcium, and the combination of TPA and the ionophore A23187. The inhibition occurred in the concentration range 1-3 microM, where no sign of cytotoxicity was noted. Preincubation for 5-10 min was needed for inhibition, and the effect persisted after washing of the cells. No inhibition was found with optimal concentrations of the ionophore or with TPA present during the preincubation. Sphingosine in combination with suboptimal concentrations of the ionophore could induce a considerable histamine release. This response was dependent on energy and was potently inhibited by the flavonoid phloretin. After preincubation with TPA, sphingosine exerted a pronounced potentiation of the response to very low concentrations of the ionophore. The findings regarding inhibitory effects of sphingosine do not seem to be compatible with a selective action on protein kinase C. The ability to synergize with the ionophore and to potentiate the effect of preincubation with TPA resembles previous findings with palmitoylcarnitine and suggests that sphingosine can stimulate mast cells by activation of protein kinase C.