| Autor: |
Stepanenko YD; Sechenov Institute of Evolutionary Physiology and Biochemistry of the Russian Academy of Sciences, Torez pr. 44, Saint-Petersburg, Russia., Boikov SI; Sechenov Institute of Evolutionary Physiology and Biochemistry of the Russian Academy of Sciences, Torez pr. 44, Saint-Petersburg, Russia., Sibarov DA; Sechenov Institute of Evolutionary Physiology and Biochemistry of the Russian Academy of Sciences, Torez pr. 44, Saint-Petersburg, Russia., Abushik PA; Sechenov Institute of Evolutionary Physiology and Biochemistry of the Russian Academy of Sciences, Torez pr. 44, Saint-Petersburg, Russia., Vanchakova NP; Pavlov First Saint-Petersburg State Medical University, Lev Tolstoi str. 6-8, Saint-Petersburg, Russia., Belinskaia D; Sechenov Institute of Evolutionary Physiology and Biochemistry of the Russian Academy of Sciences, Torez pr. 44, Saint-Petersburg, Russia., Shestakova NN; Sechenov Institute of Evolutionary Physiology and Biochemistry of the Russian Academy of Sciences, Torez pr. 44, Saint-Petersburg, Russia., Antonov SM; Sechenov Institute of Evolutionary Physiology and Biochemistry of the Russian Academy of Sciences, Torez pr. 44, Saint-Petersburg, Russia. antonov452002@yahoo.com. |
| Abstrakt: |
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. |
