In primary prelabeled cultures of cerebellar granule cells, methyl mer
cury (MeHg) induced a concentration- and time-dependent release of [H-
3]arachidonic acid. MeHg-induced [H-3]arachidonate release was partial
ly dependent on the extracellular Ca2+ concentration. MeHg at 10-20 mu
M also stimulated basal Ca-45(2+) uptake after 20 min of incubation a
t 37 degrees C, and at 10 mu M inhibited K+ depolarization-stimulated
uptake. MeHg stimulated [H-3]arachidonate uptake, but had no effect on
the rate of phospholipid reacylation. Phospholipase A(2) (PLA(2)) act
ivation preceded cytotoxicity, but at higher concentrations of MeHg su
ch dissociation was not evident. Inhibition of MeHg-induced PLA(2) act
ivation by 100 mu M mepacrine failed to modify cytotoxicity. MeHg-indu
ced lipoperoxidation, measured as the production of thiobarbituric aci
d-reacting products, was inhibited by alpha-tocopherol without inhibit
ion of [H-3]arachidonate release. The absence of alpha-tocopherol inhi
bition of MeHg-induced arachidonate release precludes a causal role fo
r lipoperoxide-induced PLA(2) activation in this system. Moreover, MeH
g induced an increased susceptibility of unilamellar vesicles to exoge
nous PLA(2) in the presence of low Ca2+ concentrations without evidenc
e of lipid peroxidation. [H-3]Arachidonate incorporation into granule
neuron phospholipids was analyzed by isocratic HPLC analysis. Relative
ly high proportional incorporation was found in the combined phosphati
dylcholine fractions and phosphatidylinositol. With MeHg, an increase
in the relative specific activity of incorporation was found in the ph
osphatidylinositol fraction, indicating a preferential turnover in thi
s phospholipid species in the presence of MeHg.