Effect of ganglioside GM1 on arachidonic acid release in bovine aortic endothelial cells

A role for the ganglioside GM1 in arachidonic acid release in bovine aortic endothelial cells (BAEC) was investigated. [³H]Arachidonic acid-labeled BAEC were preincubated with GM1 and incubated with one of four different stimulators. GM1 inhibited arachidonic acid release when stimulated with maitotoxin or melittin but not with ionomycin or thapsigargin. A 10 μM GM1 concentration achieved a 50% and 100% inhibition of the maitotoxin and melittin responses, respectively. The selective inhibition displayed by GM1 on the maitotoxin and melittin responses was not due to its ability to bind calcium since all four drugs, maitotoxin, melittin, ionomycin, and thapsigargin, required extracellular calcium. The effect of GM1 was not specific to arachidonic acid release. GM1 at 50 μM inhibited phosphatidylinositol polyphosphate (PIP) hydrolysis mediated by melittin, but did not affect hydrolysis mediated by ionomycin. Moreover, the activity of GM1 was not restricted to phospholipid metabolism since it also inhibited calcium influx that was stimulated by maitotoxin or melittin but not by ionomycin. We conclude that GM1 is not a specific inhibitor of phospholipases in bovine aortic endothelial cells, but rather its activity is dependent on the type of stimulant used to activate the cell.