Abstract
In central neurons, glutamate receptor activation causes massive calcium influx and induces a mitochondrial depolarization, which is partially blocked by cyclosporin A, suggesting a possible activation of the mitochondrial permeability transition pore (PTP) as a mechanism. It has been recently reported that tamoxifen (an antiestrogen chemotherapeutic agent) blocks the PTP in isolated liver mitochondria, similar to cyclosporin A. In this study, we tested whether tamoxifen inhibits the mitochondrial depolarization induced by glutamate receptor activation in intact cultured neurons loaded with the fluorescent dye 5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethylbenzimidazolylcarbocyanine iodide. This dye reports disruptions in mitochondrial membrane potential, which can be caused by PTP activation. We found that glutamate (100 μM for 10 min) causes a robust mitochondrial depolarization that is partially inhibited by tamoxifen. The maximum inhibitory concentration of tamoxifen was 0.3 μM, with concentrations higher and lower than 0.3 μM being less effective. However, although tamoxifen (0.3 μM) blocked glutamate-induced mitochondrial depolarization, it did not inhibit glutamate-induced neuronal death, in contrast to the PTP inhibitor cyclosporin A. A relatively high concentration of tamoxifen (100 μM) caused mitochondrial depolarization itself and was neurotoxic. These data suggest that tamoxifen may be an inhibitor of the PTP in intact neurons. However, the lack of specificity of most PTP inhibitors, and the difficulty in measuring PTP in intact cells, preclude definite conclusions about the role of PTP in excitotoxic injury.
Footnotes
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Send reprint requests to: Ian J. Reynolds, Ph.D., Department of Pharmacology, University of Pittsburgh School of Medicine, E1354 Biomedical Science Tower, Pittsburgh, PA 15261. E-mail:iannmda{at}pop.pitt.edu
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↵1 This study was supported by DAMD17-98-1-8627 (to I.J.R.), the American Heart Association (to I.J.R.), AG 00751 (to D.S.H.), NS 07391 (to B.A.M.), and NS 07291 (to K.R.H.).
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↵2 Current address: Department of Neurology, 190 Medical Research Facility, 420 West 12th Ave., The Ohio State University, Columbus, OH 43210. E-mail: hoyt.31{at}osu.edu
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↵3 I.J.R. is an Established Investigator of the American Heart Association.
- Abbreviations:
- PTP
- mitochondrial permeability transition pore
- NMDA
- N-methyl-d-aspartate
- Δψm
- mitochondrial membrane potential
- JC-1
- 5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethylbenzimidazolylcarbocyanine iodide
- HBSS
- HEPES-buffered salt solution
- FCCP
- carbonyl cyanidep-trifluoromethoxyphenylhydrazone
- LDH
- lactate dehydrogenase
- Received October 11, 1999.
- Accepted January 9, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
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