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

• Published in: Scientific reports 2019-12, Vol.9 (1), p.19454-15, Article 19454
• Main Authors: Stepanenko, Yulia D., Boikov, Sergei I., Sibarov, Dmitry A., Abushik, Polina A., Vanchakova, Nina P., Belinskaia, Daria, Shestakova, Natalia N., Antonov, Sergei M.
• Format: Article
• Language: English
• Subjects: 631/378/2586; 631/378/87; 631/57/2270/1140; Amitriptyline; Amitriptyline - pharmacology; Amitriptyline - therapeutic use; Animals; Antidepressants; Antidepressive Agents, Tricyclic - pharmacology; Antidepressive Agents, Tricyclic - therapeutic use; Calcium (extracellular); Calcium - metabolism; Calcium channels (voltage-gated); Cells, Cultured; Cerebral Cortex - cytology; Channel gating; Chronic Pain - complications; Chronic Pain - diet therapy; Chronic Pain - psychology; Cytosol; Cytosol - drug effects; Cytosol - metabolism; Depression - drug therapy; Depression - etiology; Depression - psychology; Extracellular Space - drug effects; Extracellular Space - metabolism; Female; Glutamic acid receptors (ionotropic); Humanities and Social Sciences; Humans; Inhibitory Concentration 50; Ion Channel Gating - drug effects; Membrane Potentials - drug effects; multidisciplinary; N-Methyl-D-aspartic acid receptors; Neuralgia; Neuralgia - complications; Neuralgia - drug therapy; Neuralgia - psychology; Neurons - cytology; Neurons - drug effects; Neurons - metabolism; Pain; Patch-Clamp Techniques; Primary Cell Culture; Rats; Receptors, N-Methyl-D-Aspartate - antagonists & inhibitors; Receptors, N-Methyl-D-Aspartate - metabolism; Science; Science (multidisciplinary); Trapping
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-019-56072-z

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 2+ -dependent desensitization and 2) trapping channel block. Inhibition of NMDARs by ATL was found to be dependent upon external Ca 2+ concentration ([Ca 2+ ]) in a voltage-independent manner, with an IC 50 of 0.72 μM in 4 mM [Ca 2+ ]. The ATL IC 50 value increased exponentially with decreasing [Ca 2+ ], with an e -fold change observed per 0.69 mM decrease in [Ca 2+ ]. Loading neurons with BAPTA abolished Ca 2+ -dependent inhibition, suggesting that Ca 2+ affects NMDARs from the cytosol. Since there is one known Ca 2+ -dependent process in gating of NMDARs, we conclude that ATL most likely promotes Ca 2+ -dependent desensitization. We also found ATL to be a trapping open-channel blocker of NMDARs with an IC 50 of 220 µM at 0 mV. An e -fold change in ATL IC 50 was observed to occur with a voltage shift of 50 mV in 0.25 mM [Ca 2+ ]. Thus, we disclose here a robust dependence of ATL potency on extracellular [Ca 2+ ], and demonstrate that ATL bound in the NMDAR pore can be trapped by closure of the channel.