A role for the ganglioside GM1 in arachidonic acid release in bovine a
ortic endothelial cells (BAEC) was investigated. [H-3]Arachidonic acid
-labeled BAEC were preincubated with GM1 and incubated with one of fou
r different stimulators. GM1 inhibited arachidonic acid release when s
timulated with maitotoxin or melittin but not with ionomycin or thapsi
gargin. A 10 muM 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 w
as not due to its ability to bind calcium since all four drugs, maitot
oxin, melittin, ionomycin, and thapsigargin, required extracellular ca
lcium. The effect of GM1 was not specific to arachidonic acid release.
GM1 at 50 muM inhibited phosphatidyl-inositol polyphosphate (PIP) hyd
rolysis mediated by melittin, but did not affect hydrolysis mediated b
y ionomycin. Moreover, the activity of GM1 was not restricted to phosp
holipid metabolism since it also inhibited calcium influx that was sti
mulated by maitotoxin or melittin but not by ionomycin. We conclude th
at 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.