SPHINGOLIPID-GATED CA2+ RELEASE FROM INTRACELLULAR STORES OF ENDOTHELIAL-CELLS IS MEDIATED BY A NOVEL CA2+-PERMEABLE CHANNEL

Sphingolipid gated Ca2+ signaling is mediated through Ca2+-permeable channels. In this report, we characterize the properties of the channel in a human endothelial cell line (EA.hy926). Ca2+ release from intracellular stores is not antagonized by nifedipine, omega conotoxin G-VIa, or heparin. To further characterize the molecular properties of the channel, we developed a novel assay to directly measure efflux of Ca2+ from intracellular stores of permeabilized Xenopus oocytes. Following size fractionation by sucrose gradient, poly(A)(+) RNA from EA,hy926 cells is microinjected into oocytes of Xenopus laevis. We find that the mRNA encoding Ca2+ release activity is similar to 1.5-2.0 kilobases in length. The sphingolipid gated Ca2+-permeable channel is thus likely to be a novel Ca2+-permeable channel distinct from other characterized intracellular Ca2+ channels such as the ryanodyne receptor and the inositol 1,4,5-trisphosphate receptor. The method described here provides a new approach to further characterizing this channel and other intracellular Ca2+ channels.