Inhibition of NMDA-gated ion channels by bis(7)-tacrine: whole-cell and single-channel studies.
Bis(7)-tacrine is a novel dimeric acetylcholinesterase inhibitor derived from tacrine, and has been proposed as a promising agent to treat Alzheimer's disease. We have recently reported that bis(7)-tacrine prevents glutamate-induced neuronal apoptosis by antagonizing NMDA receptors. The purpose of this study was to characterize bis(7)-tacrine inhibition of NMDA-activated current by using patch-clamp recording techniques. In cultured rat hippocampal neurons, bis(7)-tacrine inhibited NMDA-activated whole-cell current in a concentration-dependent manner with an IC(50) of 0.66+/-0.07 microM. Bis(7)-tacrine produced a gradual decline of NMDA-activated current to a steady-state, but this was not an indication of use-dependence. Also, the slow onset of inhibition by bis(7)-tacrine was not apparently due to an action at an intracellular site. Bis(7)-tacrine, 0.5 microM, decreased the maximal response to NMDA by 40% without changing its EC(50). Bis(7)-tacrine inhibition of NMDA-activated current was not voltage-dependent, and was independent of glycine concentration. Results of single-channel experiments obtained from cells expressing NR1 and NR2A subunits revealed that bis(7)-tacrine decreased the open probability and frequency of channel opening, but did not significantly alter the mean open time or introduce rapid closures. These results suggest that bis(7)-tacrine can inhibit NMDA receptor function in a manner that is slow in onset and offset and noncompetitive with respect to both NMDA and glycine. The noncompetitive inhibition of NMDA receptors by bis(7)-tacrine could contribute to its protective effect against glutamate-induced neurotoxicity.
Liu
Yu-Wei
YW
Department of Neurobiology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China.
Luo
Jia-Lie
JL
Ren
Hong
H
Peoples
Robert W
RW
Ai
Yong-Xun
YX
Liu
Li-Jiang
LJ
Pang
Yuan-Ping
YP
Li
Zhi-Wang
ZW
Han
Yi-Fan
YF
Li
Chao-Ying
CY
D000818:Animals; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D004347:Drug Interactions; D004558:Electric Stimulation / Q000379:methods; D004622:Embryo, Mammalian; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology*; D006624:Hippocampus / Q000166:cytology; D015640:Ion Channel Gating / Q000187:drug effects* / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D016202:N-Methylaspartate / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000235:genetics / Q000502:physiology*; D013619:Tacrine / Q000031:analogs & derivatives* / Q000494:pharmacology; D014162:Transfection
C122128:1,7-N-heptylene-bis-9,9'-amino-1,2,3,4-tetrahydroacridine; D004791:Enzyme Inhibitors; D018690:Excitatory Amino Acid Agonists; D016194:Receptors, N-Methyl-D-Aspartate; D013619:Tacrine; D016202:N-Methylaspartate