Studies using molecular modeling, genetic engineering, neurophysiology/pharmacology, and whole animals have advanced our understanding of where and how inhaled anesthetics act to produce immobility (minimum alveolar anesthetic concentration; MAC) by actions on the spinal cord. Numerous ligand- and voltage-gated channels might plausibly mediate MAC, and specific amino acid sites in certain receptors present likely candidates for mediation. However, in vivo studies to date suggest that several channels or receptors may not be mediators (e.g., gamma-aminobutyric acid A, acetylcholine, potassium, 5-hydroxytryptamine-3, opioids, and alpha(2)-adrenergic), whereas other receptors/channels (e.g., glycine, N-methyl-D-aspartate, and sodium) remain credible candidates.

Shine and rise! GABAA–receptors are ligand-gated chloride channels that respond to the major inhibitory neurotransmitter of the mammalian central nervous system. Herein, we introduce azobenzene derivatives of propofol that increase GABA-induced currents when irradiated with light and thus function as photochromic potentiators. One of our molecules, AP2, can be employed as a light-dependent general anesthetic in translucent tadpoles.

Background Etomidate is a rapidly-acting sedative-hypnotic that provides hemodynamic stability. However because it causes prolonged suppression of adrenocortical steroid synthesis, its clinical utility and safety are limited. We describe the results of studies to define the pharmacology of (R)-3-methoxy-3-oxopropyl1-(1-phenylethyl)-1H-imidazole-5-carboxylate (MOC-etomidate), the first etomidate analogue designed to be susceptible to ultra-rapid metabolism. Methods The γ-aminobutyric acid type A receptor activities of MOC-etomidate and etomidate were compared using electrophysiological techniques in human α1β2γ2L receptors. MOC-etomidate’s hypnotic concentration was determined in tadpoles using a loss of righting reflex assay. Its in-vitro metabolic half-life was measured in human liver S9 fraction and the resulting metabolite provisionally identified using high performance liquid chromatography/mass spectrometry techniques. The hypnotic and hemodynamic actions of MOC-etomidate, etomidate, and propofol were defined in rats. The abilities of MOC-etomidate and etomidate to inhibit corticosterone production were assessed in rats. Results MOC-etomidate potently enhanced γ-aminobutyric acid type A receptor function and produced loss of righting reflex in tadpoles. Metabolism in human liver S9 fraction was first-order with an in-vitro half-life of 4.4 min versus > 40 min for etomidate. MOC-etomidate’s only detectable metabolite was a carboxylic acid. In rats, MOC-etomidate produced rapid loss of righting reflex that was extremely brief and caused minimal hemodynamic changes. Unlike etomidate, MOC-etomidate produced no adrenocortical suppression 30 minutes after administration. Conclusions MOC-etomidate is an etomidate analogue that retains etomidate’s important favorable pharmacological properties. However, it is rapidly metabolized, ultra-short acting, and does not produce prolonged adrenocortical suppression following bolus administration.

A paradox arises from present information concerning the mechanism(s) by which inhaled anesthetics produce immobility in the face of noxious stimulation. Several findings, such as additivity, suggest a common site at which inhaled anesthetics act to produce immobility. However, two decades of focused investigation have not identified a ligand- or voltage-gated channel that alone is sufficient to mediate immobility. Indeed, most putative targets provide minimal or no mediation. For example, opioid, 5-HT3, gamma-aminobutyric acid type A and glutamate receptors, and potassium and calcium channels appear to be irrelevant or play only minor roles. Furthermore, no combination of actions on ligand- or voltage-gated channels seems sufficient. A few plausible targets (e.g., sodium channels) merit further study, but there remains the possibility that immobilization results from a nonspecific mechanism.

We synthesized 2,6-Diisopropyl-4-[3-(3-methyl-3H-diazirin-3-yl)-propyl]-phenol (p-(4-azipentyl)-propofol), or p-4-AziC5-Pro, a novel photoactivable derivative of the general anesthetic propofol. p-4-AziC5-Pro has an anesthetic potency similar to propofol. Like propofol, the compound potentiates inhibitory GABAA receptor current responses and allosterically modulates binding to both agonist and benzodiazepine sites, assayed on heterologously expressed GABAA receptors. p-4-AziC5-Pro inhibits excitatory current responses of nACh receptors expressed in Xenopus oocytes and photoincorporates into native nACh receptor-enriched Torpedo membranes. Thus p-4-AziC5-Pro is a functional general anesthetic that both modulates and photoincorporates into Cys-loop ligand-gated ion channels, making it an excellent candidate for use in identifying propofol binding sites.

Serotonin type 3 (5-HT 3 ) receptors are members of the pentameric Cys-loop superfamily of receptors that modulate synaptic neurotransmission. In response to agonist binding and unbinding, members of this superfamily undergo a series of conformational transitions that define their functional properties. In this study, we report the results of electrophysiological studies using rapid solution exchange designed to characterize and compare the actions of the high-efficacy agonist serotonin and the low-efficacy agonist dopamine on human 5-HT 3A receptors expressed in human embryonic kidney HEK293 cells. In the case of serotonin, receptor activation rates varied with agonist concentration, and deactivation occurred as a single-exponential process with a rate that was similar to the maximal rate of desensitization. Receptors recovered slowly from long desensitizing pulses of serotonin with a sigmoidal time course. In the case of dopamine, receptor activation rates were independent of agonist concentration, receptor deactivation occurred as a complex process that was significantly faster than the maximal rate of desensitization, and recovery from desensitization occurred more quickly than with 5-HT and its time course was not sigmoidal. We developed an allosteric kinetic model for 5-HT 3A receptor activation, deactivation, desensitization, and resensitization. Interpretation of our results within the context of this model indicated that the distinct modulatory actions of serotonin versus dopamine are largely attributable to the vastly different rates with which these two agonists induce channel opening and dissociate from open and desensitized states.

N-Methyl-d-aspartate (NMDA) receptors have a presumed role in excitatory synaptic transmission and nociceptive pathways. Although previous studies have found that inhaled anesthetics inhibit NMDA receptor-mediated currents at clinically relevant concentrations, the use of different experimental protocols, receptor subtypes, and/or tissue sources confounds quantitative comparisons of the NMDA receptor inhibitory potencies of inhaled anesthetics. In the present study, we sought to fill this void by defining, using the two-electrode voltage-clamp technique, the extent to which diverse clinical and aromatic inhaled anesthetics inhibit the NR1/NR2B subtype of the human NMDA receptor expressed in Xenopus laevis oocytes. At 1 minimum alveolar anesthetic concentration (MAC), anesthetic compounds reversibly inhibited NMDA receptor currents by 12 +/- 6% to 74 +/- 6%. These results demonstrate that equianesthetic concentrations of inhaled anesthetics can differ considerably in the extent to which they inhibit NMDA receptors. Such differences may be useful for defining the role that this receptor plays in producing the in vivo actions of general anesthetics.

Shine and rise! GABA A -receptors are ligand-gated chloride channels that respond to the major inhibitory neurotransmitter of the mammalian central nervous system. Herein, we introduce azobenzene derivatives of propofol that increase GABA-induced currents when irradiated with light and thus function as photochromic potentiators. One of our molecules, AP2, can be employed as a light-dependent general anesthetic in translucent tadpoles. Keywordspropofol; azobenzenes; GABA receptors; photopharmacology GABA A receptors are pentameric ligand-gated ion channels that are activated by the major inhibitory neurotransmitter in the mammalian brain, γ-aminobutyric acid (GABA). [1] Binding of GABA results in the opening of a chloride ion-selective pore, thusCorrespondence to: Erwin Sigel, erwin.sigel@mci.unibe.ch; Dirk Trauner, dirk.trauner@lmu.de. 1 These authors contributed equally to this work.Supporting information for this article is available on the WWW under http://www.angewandte.org or from the author. hyperpolarizing the postsynaptic neuron and decreasing the likelihood of action potential firing. As such, GABA A receptors are a prominent target for anesthetic, hypnotic, and anticonvulsant drugs (Fig. 1). [2,3] While agonists, antagonists and blockers of GABA A receptors, such as muscimol, gabazine, or picrotoxinin, respectively, have proven to be valuable research tools, their impact on human medicine has been limited. Drugs that target these receptors are dominated by allosteric modulators that potentiate, i.e. increase, chloride currents elicited by the neurotransmitter. Well-established potentiators include benzodiazepines (e.g. diazepam), barbiturates (e.g. phenobarbital), the imidazopyridine zolpidem and the simple phenol propofol. [2] These bind to distinct allosteric sites on GABA A receptors increasing the mean open time or the opening frequency of the channel. However, the analysis of their exact binding sites at a molecular level has been complicated by a lack of detailed structural data. NIH Public AccessFollowing its discovery in 1980, propofol has become the most widely used intravenous general anaesthetic. [4] Although its mode of action has not been fully elucidated, it is commonly accepted that the anaesthesia induced by this unusually lipophilic drug mostly results from potentitation of GABA-induced currents, as well as a direct activation of the chloride channel at low concentrations. Propofol has a rapid onset and offset of action and shows only minimal accumulation upon prolonged use. The intravenous administration of propofol is also associated with reduced postoperative nausea and vomiting. [5] While GABA A -receptors respond to a variety of ligands, they are normally not sensitive toward light. It would be fascinating to confer light-sensitivity to these ion channels, since light is unsurpassed in terms of the temporal and spatial precision it provides. This could be indirectly achieved via ligands that act on the receptors but can be optically switched between an active and an inacti...