Abstract
2-Aminoethyl methylphosphonate (2-AEMP), an analog of GABA, has been found to exhibit antagonist activity at GABAA-ρ1 (also known as ρ1 GABAC) receptors. The present study was undertaken to elucidate 2-AEMP's action and to test the activities of 2-AEMP analogs. Whole-cell patch-clamp techniques were used to record membrane currents in neuroblastoma cells stably transfected with human GABAA-ρ1 receptors. The action of 2-AEMP was compared with that of 1,2,5,6-tetrahydropyridin-4-yl methylphosphinic acid (TPMPA), a commonly used GABAA-ρ1 antagonist. With 10 μM GABA, 2-AEMP's IC50 (18 μM) differed by less than 2.5-fold from that of TPMPA (7 μM), and results obtained were consistent with a primarily competitive mode of inhibition by 2-AEMP. Terminating the presentation of 2-AEMP or TPMPA in the presence of GABA produced a release from inhibition. However, the rate of inhibition release upon the termination of 2-AEMP considerably exceeded that determined with termination of TPMPA. Moreover, when presented at concentrations near their respective IC50 values, the preincubation period associated with 2-AEMP's onset of inhibition was much shorter than that for TPMPA. Analogs of 2-AEMP possessing a benzyl or n-butyl rather than a methyl substituent at the phosphorus atom, as well as analogs bearing a C-methyl substituent on the aminoethyl side chain, exhibited reduced potency relative to 2-AEMP. Of these analogs, only (R)-2-aminopropyl methylphosphonate significantly diminished the response to 10 μM GABA. Structure-activity relationships are discussed in the context of molecular modeling of ligand binding to the antagonist binding site of the GABAA-ρ1 receptor.
Footnotes
This work was supported by the National Institutes of Health National Eye Institute [Grants EY016094, EY001792]; the National Institutes of Health National Heart, Lung, and Blood Institute [Grant HL024530]; the Daniel F. and Ada L. Rice Foundation; Hope for Vision; the Macular Degeneration Research Program of the American Health Assistance Foundation; the Arnold and Mabel Beckman Initiative for Macular Research; Research to Prevent Blindness; and the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the United States Department of Energy.
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
doi:10.1124/mol.111.071225.
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ABBREVIATIONS:
- TPMPA
- 1,2,5,6-tetrahydropyridin-4-yl methylphosphinic acid
- 2-AEMP
- 2-aminoethyl methylphosphonate
- 3-APMPA
- 3-aminopropyl methylphosphinic acid
- s-Bu
- secondary butyl
- Cbz
- carbobenzyloxy
- DCM
- dichloromethane
- DEAD
- diethyl azodicarboxylate
- DIPEA
- N,N-diisopropylethylamine
- THF
- tetrahydrofuran
- TLC
- thin-layer chromatography
- trityl
- triphenylmethyl.
- Received January 14, 2011.
- Accepted August 2, 2011.
- U.S. Government work not protected by U.S. copyright
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