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 μM 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.

Tricyclic Antidepressant Structure-Related Alterations in Calcium-Dependent Inhibition and Open-Channel Block of NMDA Receptors

“…To overcome this contradiction, one may suggest an existence of different mechanisms of TCA-inhibition of NMDARs. In agreement, we have recently demonstrated that regardless of the openchannel block, ATL additionally induces a calcium-dependent and voltage-resistant inhibition of NMDARs since the increase of calcium concentration in the extracellular solution substantially enforces the NMDAR inhibition by ATL (Stepanenko et al, 2019). Some similar effects on NMDARs could be achieved by ethanol (Boikov et al, 2020) and lithium or by an inhibitor (KB-R7943) of Na + / Ca 2+ -exchangers (Sibarov et al, 2015), which all as known can provoke the calcium-dependent desensitization of NMDARs (Sibarov et al, 2015).…”

“…To obtain the voltage-dependence of NMDAR block by TCAs, the concentration-ihibition curves were generated at three membrane holding potentials V m = −100, −70, and −30 mV. The obtained values were fitted with the modified by incorporating the dependence of NMDAR inhibition on [Ca 2+ ] (Stepanenko et al, 2019) Woodhull equation:…”

Amitriptyline Decreases GABAergic Transmission in Basal Forebrain Neurons Using an Optogenetic Model of Aging

“…It also acts to block Ca 2+ and Na + channels (Brau et al, 2001;Nicholson et al, 2002;Yan et al, 2010;Wu et al, 2012). Additional actions of AMI are described for the NMDA receptor ion channel complex that may contribute to efficacy against neuropathic pain, including the enhancement of Ca 2+ -dependent receptor desensitization and acting as an open channel blocker of NMDARs (Stepanenko et al, 2019 0.63 mM (Stepanenko et al, 2019). These actions on the NMDA receptor provide a likely mechanism for results showing that AMI inhibited the NMDA-dependent LTP in the hippocampus (Watanabe et al, 1993).…”

Inhibition of N-type calcium ion channels by tricyclic antidepressants – experimental and theoretical justification for their use for neuropathic pain

“…28,29 Cilnipidine was used as a positive control. 30 The test compounds (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13) were chosen based on a number of criteria. Firstly, the TCAs examined by Lavoie et al (1)(2)(3)(4) were included.…”

“…Five other TCAs, doxepin (7), protriptyline (8), opipramol (9), maprotiline (10) and amoxapine (11), were chosen as these drugs are commonly prescribed tricyclic antidepressants in Australia 31 and the United States 32 and/or Europe. Finally, two structurally-related drugs, the muscle relaxant cyclobenzaprine (12) and the sedating antihistamine promethazine (13) were also tested. The purpose of choosing a wide set of TCAs for study was to gauge the generality of the Ca V 2.2 blockade by this class of drug and to look for any obvious structure-activity relationships.…”