Mechanism-based approach to the successful prevention of cocaine inhibition of the neuronal (alpha 3 beta 4) nicotinic acetylcholine receptor.
The nicotinic acetylcholine receptor (nAChR) belongs to a family of five channel-forming proteins that regulate communication between the approximately 10(12) cells of the nervous system. A minimum mechanism of inhibition of the muscle-type nAChR (1) by the noncompetitive inhibitors cocaine and MK-801 [(+)-dizocilpine, an anticonvulsant] indicated they bind to a regulatory site, with higher affinity for the closed-channel form than for the open-channel form, thus shifting the equilibrium toward the closed-channel form and inhibiting receptor function. The mechanism predicts that compounds that bind to this regulatory site with equal or higher affinity for the open-channel conformation than for the closed-channel conformation will prevent receptor inhibition (1). Does a neuronal form of the receptor behave similarly? The mechanism of inhibition of the neuronal nAChR by cocaine and MK-801 using rapid chemical kinetic techniques was investigated. The alpha3beta4 nAChR stably expressed in HEK 293 cells was used in these investigations. Whole-cell currents originated from a major and minor nAChR isoform. Only the major isoform has been characterized. For the dominant, rapidly desensitizing isoform, the carbamoylcholine dissociation constant for the site controlling receptor activation, Kd, is 2 mM; the channel-opening equilibrium constant, Phi(-1), is 4; and the dominant desensitization rate constant, k34, is 20 s(-1). Cocaine inhibits the receptor noncompetitively, with an apparent KI of 84 and 26 microM at high and low carbamoylcholine concentrations, at which concentrations the receptor is mainly in the open- or closed-channel form, respectively. Similar results were obtained with MK-801. A combinatorially synthesized RNA ligand and a cocaine analogue alleviated cocaine inhibition of this neuronal receptor.
Krivoshein
Arcadius V
AV
Department of Molecular Biology and Genetics, 216 Biotechnology Building, Cornell University, Ithaca, New York 14853-2703, USA.
Hess
George P
GP
D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D002217:Carbachol / Q000494:pharmacology; D002460:Cell Line; D003042:Cocaine / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D016291:Dizocilpine Maleate / Q000494:pharmacology; D006801:Humans; D009433:Neural Inhibition / Q000187:drug effects*; D009469:Neuromuscular Junction / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D018722:Nicotinic Agonists / Q000494:pharmacology; D018733:Nicotinic Antagonists / Q000378:metabolism* / Q000494:pharmacology; D011487:Protein Conformation / Q000187:drug effects; D021122:Protein Subunits / Q000819:agonists / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D051381:Rats; D011978:Receptors, Nicotinic / Q000737:chemistry* / Q000378:metabolism*
D018722:Nicotinic Agonists; D018733:Nicotinic Antagonists; D021122:Protein Subunits; D011978:Receptors, Nicotinic; C403530:nicotinic receptor alpha3beta4; D016291:Dizocilpine Maleate; D002217:Carbachol; D003042:Cocaine