Abstract
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.
Footnotes
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Send reprint requests to: Philip Lazarovici, Department of Pharmacology and Experimental Therapeutics, School of Pharmacy, Faculty of Medicine, The Hebrew University of Jerusalem, P.O. Box 12065, Jerusalem 91120, Israel.
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↵1 Affiliated with the David R. Bloom Center for Pharmacy at the Hebrew University.
- Abbreviations:
- PX
- pardaxin
- BPB
- 4-bromophenacyl bromide
- CCH
- carbachol
- [Ca]o
- extracellular calcium
- [Ca]i
- cytosolic-free calcium
- Dan
- dantrolene
- NDGA
- nordihydroguaiaretic acid
- AA861
- 2-(12-hydroxydodeca-5,10-diynyl)-3,5,6-trimethyl-1,4-benzoquinone
- AA
- arachidonic acid
- 5-HETE
- 5-hydroxyeicosatetranoic acid
- Fura-2-AM
- acetoxymethyl ester of Fura-2
- DMEM
- Dulbecco’s modified Eagle’s medium
- PC12
- pheochromocytoma cells
- BAPTA
- 1,2-bis(2-aminophenoxy)ethane-N,N,N′N′-tetra-acetic acid
- PLA2
- phospholipase A2
- IP3
- inositol 1,4,5-trisphosphate
- Received October 1, 1997.
- Accepted August 5, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
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