Abstract
The opioid peptide dynorphin A elicits non-opioid receptor-mediated, neurotoxic response in vivo, which is blocked by pretreatment with MK-801, a noncompetitiveN-methyl-d-aspartate receptor (NMDAR) antagonist. In the present study, we examined the possible direct interaction of dynorphin A on the NMDAR. A nonopioid dynorphin A analog, 125I-(des-tyrosyl) dynorphin A(2-17), was used in radioligand binding analysis on rat cortical brain membranes. This radioligand exhibited a saturable, specific binding at high affinity with a Kd value of 9.4 ± 1.6 nM and maximal binding of 2.4 ± 0.6 pmol/mg protein. This binding site was associated with the NMDAR complex because it was modulated by a number of NMDAR ligands. Transient expression of the rat NR1a/NR2A complex in human embryonic kidney 293 cells confirmed a coexpression of125I-(des-tyrosyl) dynorphin A(2-17), [3H]CGP39,653, and [3H]MK-801 binding. These data provide direct evidence of the presence of a high-affinity binding site for dynorphin A on the NMDAR. The modulatory effect of the various NMDAR-selective ligands on dynorphin A binding suggests that dynorphin A may bind preferentially to the closed/desensitized state of the NMDAR. The physiological role of dynorphin A binding to the NMDAR remains to be established.
Footnotes
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Send reprint requests to: Josephine Lai, Ph.D., Department of Pharmacology, The University of Arizona Health Sciences Center, Tucson, AZ 85724. E-mail: lai{at}u.arizona.edu
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↵1 This work was supported by National Institutes of Health Grants DA11823 and DA04248.
- Abbreviations:
- NMDAR
- N-methyl-d-aspartate receptor
- HEK
- human embryonic kidney
- CKA
- 7-chlorokynurenic acid
- PMSF
- phenylmethylsulfonyl fluoride
- BSA
- bovine serum albumin
- RP
- reverse phase
- HBS
- HEPES-buffered saline
- Received April 27, 1999.
- Accepted July 29, 1999.
- The American Society for Pharmacology and Experimental Therapeutics