Vol. 288, Issue 2, 399-406, February 1999

Characterization of Pardaxin-Induced Dopamine Release from Pheochromocytoma Cells: Role of Calcium and Eicosanoids

Saleh Abu-Raya, Eugenia Bloch-Shilderman, Peter I. Lelkes, Victoria Trembovler, Esther Shohami, Yehuda Gutman and Philip Lazarovici¹

Department of Pharmacology and Experimental Therapeutics, School of Pharmacy, Faculty of Medicine, The Hebrew University of Jerusalem, Jerusalem 91120, Israel (S.A.-R., E.B.-S., V.T., E.S., Y.G., P.L.); and Laboratory of Cell Biology, University of Wisconsin, Medical School, Milwaukee Clinical Campus, Milwaukee, Wisconsin (P.I.L)

Pardaxin, an excitatory neurotoxin, induced dopamine release from pheochromocytoma (PC12) cells both in the presence and absence of extracellular calcium ([Ca]_o). In the presence of extracellular calcium, nifedipine, an L-type calcium channel blocker, did not affect dopamine release, whereas 1,2-bis (2-aminophenoxy) ethane N,N, N'N'-tetra-acetic acid (BAPTA), a chelator of cytosolic calcium, and dantrolene, a blocker of calcium release from intracellular stores, inhibited only partially (30-40%) pardaxin-induced dopamine release. In the absence of [Ca]_o, BAPTA and dantrolene were ineffective. Pardaxin stimulated the arachidonic acid (AA) cascade in PC12 cells independently of [Ca]_o. The phospholipase inhibitors mepacrine and bromophenacyl bromide inhibited both pardaxin-induced AA release and pardaxin-induced dopamine release. Dopamine release induced by pardaxin also was blocked by the lipoxygenase inhibitors nordihydroguaiaretic acid, esculetin, and 2-(12-hydroxydodeca-5,10-diynyl)-3,5,6-trimethyl-1,4-benzoquinone. Under these conditions, a parallel reduction in 5-hydroxyeicosatetranoic acid release also was observed. Suppression of pardaxin-induced dopamine release by inhibitors of phospholipase A₂ and lipoxygenase was more pronounced in calcium-free medium. These results indicate the involvement of the lipoxygenase pathway in pardaxin-induced dopamine release and suggest the use of this toxin as a novel pharmacological tool for investigating the mechanism of calcium-independent neurotransmitter release.