The
lipoxygenase product 12-hydroperoxy-5,8,10,14-eicosatetraenoic
acid (12-HPETE), stimulates the synaptic response produced by the modulatory transmitter
histamine and the neuroactive
peptide Phe-Met-Arg-Phe-amide (
FMRFamide) in identified neurons of the marine mollusk Aplysia californica. The
12-lipoxygenase pathway has not yet been fully characterized, but
12-HPETE is known to be metabolized further. Therefore, we began to search for other metabolites in order to investigate whether the actions of
12-HPETE might require its conversion to other active products. We have identified 12-keto-5,8,10,14-eicosatetraenoic
acid (12-KETE) as a metabolite of
12-HPETE formed by Aplysia nervous tissue.
12-KETE was identified in incubations of the tissue with
arachidonic acid using HPLC, UV spectrometry, and gas-chromatography/mass spectrometry. [3H]12-KETE is formed from endogenous
lipid stores in nervous tissue, labeled with [3H]
arachidonic acid upon stimulation by application of
histamine. In L14 and L10 cells, identified neurons in the abdominal
ganglion, applications of
12-KETE elicit changes in membrane potential similar to those evoked by
histamine. Another metabolite of
12-HPETE, 12(s)-hydroxy-5,8,10,14-eicosatetraenoic
acid [12(S)-
HETE], is inactive. These results support the hypothesis that
12-HPETE and its metabolite,
12-KETE, participate in transduction of
histamine responses in Aplysia neurons.