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Dual action of amitriptyline on NMDA receptors: enhancement of Ca-dependent desensitization and trapping channel block.

ABSTRACT: Although the tricyclic antidepressant amitriptyline (ATL) is widely used in the clinic, the mechanism underlying its high therapeutic efficacy against neuropathic pain remains unclear. NMDA receptors (NMDARs) represent a target for ATL and are involved in sensitization of neuropathic pain. Here we describe two actions of ATL on NMDARs: 1) enhancement of Ca2+-dependent desensitization and 2) trapping channel block. Inhibition of NMDARs by ATL was found to be dependent upon external Ca2+ concentration ([Ca2+]) in a voltage-independent manner, with an IC50 of 0.72??M in 4?mM [Ca2+]. The ATL IC50 value increased exponentially with decreasing [Ca2+], with an e-fold change observed per 0.69?mM decrease in [Ca2+]. Loading neurons with BAPTA abolished Ca2+-dependent inhibition, suggesting that Ca2+ affects NMDARs from the cytosol. Since there is one known Ca2+-dependent process in gating of NMDARs, we conclude that ATL most likely promotes Ca2+-dependent desensitization. We also found ATL to be a trapping open-channel blocker of NMDARs with an IC50 of 220?µM at 0?mV. An e-fold change in ATL IC50 was observed to occur with a voltage shift of 50?mV in 0.25?mM [Ca2+]. Thus, we disclose here a robust dependence of ATL potency on extracellular [Ca2+], and demonstrate that ATL bound in the NMDAR pore can be trapped by closure of the channel.

SUBMITTER: Stepanenko YD

PROVIDER: S-EPMC6923474 | biostudies-literature | 2019 Dec

REPOSITORIES: biostudies-literature

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Dual action of amitriptyline on NMDA receptors: enhancement of Ca-dependent desensitization and trapping channel block.

Stepanenko Yulia D YD Boikov Sergei I SI Sibarov Dmitry A DA Abushik Polina A PA Vanchakova Nina P NP Belinskaia Daria D Shestakova Natalia N NN Antonov Sergei M SM

Scientific reports 20191219 1

Although the tricyclic antidepressant amitriptyline (ATL) is widely used in the clinic, the mechanism underlying its high therapeutic efficacy against neuropathic pain remains unclear. NMDA receptors (NMDARs) represent a target for ATL and are involved in sensitization of neuropathic pain. Here we describe two actions of ATL on NMDARs: 1) enhancement of Ca<sup>2+</sup>-dependent desensitization and 2) trapping channel block. Inhibition of NMDARs by ATL was found to be dependent upon external Ca< ...[more]

PMID: 31857688

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Project description:Memantine and ketamine are clinically useful NMDA receptor (NMDAR) open channel blockers that inhibit NMDARs with similar potency and kinetics, but display vastly different clinical profiles. This discrepancy has been hypothesized to result from inhibition by memantine and ketamine of overlapping but distinct NMDAR subpopulations. For example, memantine but not ketamine may inhibit extrasynaptic NMDARs more effectively than synaptic NMDARs. However, the basis for preferential NMDAR inhibition depending on subcellular location has not been investigated systematically. We integrated recordings from heterologously expressed single NMDAR subtypes, kinetic modeling, and recordings of synaptically evoked NMDAR responses in acute brain slices to investigate mechanisms by which channel blockers may distinguish NMDAR subpopulations. We found that memantine and ketamine differentially alter NMDAR desensitization and that memantine stabilizes a Ca2+-dependent desensitized state. As a result, inhibition by memantine of GluN1/2A receptors in tsA201 cells and of native synaptic NMDARs in cortical pyramidal neurons from mice of either sex increased in conditions that enhanced intracellular Ca2+ accumulation. Therefore, differential inhibition by memantine and ketamine based on NMDAR location is likely to result from location dependence of the intensity and duration of NMDAR activation. Modulation of Ca2+-dependent NMDAR desensitization is an unexplored mechanism of inhibitory action with the potential to endow drugs with NMDAR selectivity that leads to superior clinical profiles. Our results suggest that designing compounds to target specific receptor states, rather than specific receptor types, may be a viable strategy for future drug development.SIGNIFICANCE STATEMENT Memantine and ketamine are NMDA receptor (NMDAR) channel-blocking drugs with divergent clinical effects. Understanding mechanistically their differential actions may advance our understanding of nervous system disorders and suggest strategies for the design of more effective drugs. Here, we show that memantine and ketamine have contrasting effects on NMDAR desensitization. Ketamine binding decreases occupancy of desensitized states of the GluN1/2B NMDAR subtype. In contrast, memantine binding increases occupancy of GluN1/2A and native NMDAR desensitized states entered after accumulation of intracellular Ca2+, a novel inhibitory mechanism. These properties may contribute to inhibition of distinct NMDAR subpopulations by memantine and ketamine and help to explain their differential clinical effects. Our results suggest stabilization of Ca2+-dependent desensitized states as a new strategy for pharmaceutical neuroprotection.

Dataset Information

Dual action of amitriptyline on NMDA receptors: enhancement of Ca-dependent desensitization and trapping channel block.

Publications

Dual action of amitriptyline on NMDA receptors: enhancement of Ca-dependent desensitization and trapping channel block.

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