New Approaches to Stretched Film Sample Alignment and Data Collection for Vibrational Linear Dichroism

Rapid measurements of vibrational linear dichroism (VLD) infrared spectra are shown to be possible by using stretched polymer films and an extension of existing instrumentation designed for vibrational circular dichroism spectroscopy. Earlier techniques can be extended using additional inexpensive polymer substrates to record good-quality VLD spectra of a significantly wider range of compounds with comparatively short sample-preparation times. The polymer substrates used, polyethylene and polytetrafluoroethylene, are commonly available and inexpensive, and samples are more easily prepared than that for many earlier stretched-film and crystal studies. Data are presented for neutral hydrophobic organic molecules on hydrophobic films including acridine, anthracene, fluorene, and recently synthesized S-(4-((4-cyanophenyl)ethynyl)phenyl)ethanethioate. We extend the approach to polar or ionic species, including 2,2'-bipyridine, 1,10-phenanthroline, and sodium dodecyl sulfate, by oxidizing polyethylene films to change their wetting properties. The combination of new instrumentation and modified sample preparation methods is useful in basic spectroscopy for untangling and assigning complicated infrared spectra. Nevertheless, it is not a panacea as surface-adsorbed molecules are often not monodispersed, and higher analyte concentrations can lead to aggregation and resonance phenomena that have previously been observed for infrared spectra on surfaces. These effects can be assessed by varying the sample concentration. The focus of this paper is experimental, and detailed analysis of most of the spectra lies outside its scope, including some well-studied compounds such as acridine and anthracene that allow comparisons with earlier research.

Composting and vermicomposting of sewage sludge at various C/N ratios: Technological feasibility and end-product quality

Even though sewage sludge (SS) contains a high level of pollutants, it is rich in essential plant nutrients and has the potential to enhance soil fertility. However, the SS must be further treated through pre-composting plus vermicomposting to make it safe for use on food crops. More research and data are needed to determine how different carbon-to-nitrogen ratios (C/N) affect the feasibility and quality of composting vs vermicomposting of SS. Therefore, in this study we comprehensively evaluated the feasibility and end-product quality of compost and vermicompost produced from SS under different C/N ratios. SS was mixed with pelletized wheat straw (PWS) at various proportions to produce C/N ratios of 6:1, 18:1, 28:1, and 38:1, then pre-composted for 14 days followed by vermicomposting using the earthworm Eisenia andrei for 120 days. Agrochemical properties were measured at 0, 30, 60, 90, and 120 days. Results revealed significantly higher levels of agrochemicals in vermicompost compared to compost, including total potassium (37-88%) and magnesium (4.3-12%), nitrate nitrogen (71-98%), available potassium (53-88%), available phosphorus (79%), available magnesium (54-453%), available boron (48-303%), and available copper (2.5-82%). However, lower levels of ammonium nitrogen by (59-85%), available iron (2.3-51.3%), available manganese (29.7-52.2%), available zinc (10.5-29.8%), total carbon (0.75-4.5%), and total nitrogen (1.6-22.2%) were measured. Comparison of the various C/N ratios, showed that vermicompost with an 18:1 C/N ratio outperformed compost and demonstrated the highest earthworm population (165 pieces/kg). Thus, vermicomposting SS at an 18:1 C/N ratio is strongly recommended as a sustainable technology for producing high-quality vermicompost from SS.

Conformational analysis of amphetamine and methamphetamine: a comprehensive approach by vibrational and chiroptical spectroscopy

After cannabis, the most commonly used illicit substance worldwide is amphetamine and its derivatives, such as methamphetamine, with an ever-increasing number of synthetic modifications. Thus, fast and reliable methods are needed to identify them according to their spectral patterns and structures. Here, we have investigated the use of molecular spectroscopy methods to describe the 3D structures of these substances in a solution that models the physiological environment. The substances were analyzed by Raman and infrared (IR) absorption spectroscopy and by chiroptical methods, vibrational circular dichroism (VCD) and Raman optical activity (ROA). The obtained experimental data were supported by three different computational approaches based on density functional theory (DFT) and molecular dynamics (MD). Successful interpretation relies on good agreement between experimental and predicted spectra. The determination of the conformer populations of the studied molecules was based on maximizing the similarity overlap of weighted conformer spectra by a global minimization algorithm. Very good agreement was obtained between the experimental spectra and optimized-population weighted spectra from MD, providing a detailed insight into the structure of the molecules and their interaction with the solvent. The relative population of three amphetamine and six methamphetamine conformers was determined and is consistent with a previous NMR study. However, this work shows that only a few isolated conformers are not sufficient for the successful interpretation of the spectra, but the entire conformational space needs to be sampled appropriately and explicit interaction with the solvent needs to be included.

Nutrient recovery and changes in enzyme activity during vermicomposting of hydrolysed chicken feather residue

Chicken feathers are hazardous to the environment because of their poor digestibility and potential as a source of environmental contaminants. However, this waste contains valuable plant nutrients that can be recovered and used to improve soil fertility and agricultural productivity. The objectives of this study were to evaluate how effective vermicomposting is at recovering nutrients and changes in enzymatic activity during vermicomposting of hydrolysed chicken feather residues (HCFR). The study included four treatments with three replications at different HCFR and pelletized wheat straw (PWS) mixing proportions: (T1) 25% HCFR+75% PWS with earthworms, (T2) 25% HCFR+75% PWS without earthworms, (T3) 50% HCFR+50% PWS with earthworms, and (T4) 50% HCFR+50% PWS (w/w) without earthworms. Eisenia andrei was used in the experiment for 120 days. Earthworm treatments recovered more available plant nutrients than non-earthworm treatments by 14% N - NO 3 - (T1); 50% K (T3); 47% Mg (T3); 75% P (T3); 55% B (T3); 34% Cu (T3); 40% Fe (T1); 46% Mn (T3); 11% Zn (T1). However, N - NH 4 + was significantly reduced by -80% (T1). Acid phosphatase, arylsulphatase, alanine aminopeptidase, and leucine aminopeptidase were more active in the treatments with earthworms and positively correlated with P and C: N ratio. Alanine aminopeptidase (3752 µmol AMCA.g-1.h-1) and leucine aminopeptidase (4252 µmol AMCL.g-1.h-1) had higher activities in T3 on day 60 of vermicomposting. As a result, the earthworm treatment recovers more plant nutrients than the non-earthworm treatments, and it can be recommended as a better vermicomposting approach for nutrient recovery from HCFR.

Low-frequency Raman Optical Activity Provides Insight into Structure of Chiral Liquids

Vibrational frequencies of modes involving intermolecular motions in liquids are relatively small, in the Raman scattering close to the excitation frequency, and the bands may merge into a diverging uninterpretable...

Chiral detection by induced surface-enhanced Raman optical activity

Combination of optical activity with surface-enhanced Raman scattering has been a dream of physical chemists for a long time. We report a measurement protocol based on silver colloids and aromatic linkers where chiral acids could be detected in concentrations of about 10-5 M. We explain the mechanism by binding and self-assembly of the linkers into chiral aggregates on the silver surface. Following the "sergeants-and-soldiers" principle, the chirality is determined by the relatively minor acidic component. Such detection of biologically relevant molecules may be useful when other methods, such as electronic circular dichroism, are not sensitive enough. In the future, variations of the chemical structure of the linker or other conditions are needed to provide a more specific signal allowing one to better discriminate among the optically active molecules.

Thermal thickening of nitrified liquid phase of digestate for production of concentrated complex fertiliser and high-quality technological water

Large production of liquid phase of digestate (LPD) characterised by low dry matter content increases the costs of LPD storage and transportation. Additionally, significant nitrogen losses result from LPD handling. The operation of biogas plants also requires large amounts of technological water, a scarce resource. The method of LPD nitrification and subsequent thermal thickening as a promising alternative treatment able to overcome those problems was investigated. The properties of thermally thickened nitrified LPD and of the distillate derived from vacuum evaporation of nitrified LPD were examined. The results show that over 99.9% of nitrogen was accumulated in thickened nitrified LPD. Total nitrogen (TN) concentration in thickened LPD ranged from 12 to 18 g/L depending on the distillate/thickened LPD volume ratio applied. The thickened LPD was also richer in other nutrients, which indicates its possible use as a concentrated complex fertiliser. TN concentration and conductivity in the distillate did not exceed 6 mg/L and 0.03 mS/m respectively, suggesting that the distillate may be useful as alternative source of technological water. It was concluded that the system consisting of nitrification and subsequent thermal thickening of nitrified LPD yields final products exhibiting significantly superior properties compared to thermal thickening of raw LPD, without requiring any additional chemical agents. The quality of these products is comparable to those obtained through advanced membrane processes.

[Innovated Judet Ribs Plates - Preclinical Study, First Clinical Experience]

PURPOSE OF THE STUDY Based on the experience with using the Judet plates in stabilization of rib fractures an innovated Judet plate was constructed in cooperation with the Development Department of Medin company. During the preclinical part of the project, following the construction of the new Judet plate, a surgical technique was elaborated. Subsequently, the clinical application of rib osteosynthesis with innovated plates was commenced. MATERIAL AND METHODS In the course of the last three years the innovated Judet rib plate including the instruments were constructed by the Development Department of Medin company in cooperation with the Trauma Centre and the Department of Surgery of the University Hospital Královské Vinohrady. The goal of the innovation was the changes in technical parameters of rib plates which are compared with the new plates of other companies: 1. Adequate plate stability along the rib axis. 2. Creation of fixation clips for a stable, but not traumatized fixation of the plate around the rib. 3. Decreased robustness of the plate with sufficient stiffness. 4. Working out of a new technique of plate fixation with the use of new instruments. 5. Ensuring plate fixation with cortical locking screws. In the preclinical part of the project osteosynthesis of the broken rib was performed with a plate on a chest model for the basic types of rib fractures. Subsequently, the plate was used for rib osteosynthesis in a cadaver. The goal of the new instruments was besides temporarily maintaining the rib fracture reduction also the subsequent temporary application of plates with the assistance of fixation tongs before the final fixation of plates. In 2017, the clinical part of the project on the stabilisation of flail chest with the innovative Judet plates was launched. This type of innovative Judet plates has so far been used in 3 patients. RESULTS As to the surgical technique of ribs osteosynthesis: The profile of the plate has been adapted to the rib profile and can be further adjusted to rib curvature, also the fixation shoulders of the plates have been reshaped. The innovated plate has been complemented with a new configuration of fixation clips and the possibility to fix the plate with locking screws. The used cortical locking screws enable appropriate stabilisation of plates. They were tested on a laboratory model of ribs and on a cadaver using the new set of instruments. The plates can be easily shaped with tongs. The anchorage of fixation clips is adequately provided for also by means of tongs. The plates can be fixed to the rib without any significant compression of intercostal nerves. The essential change of the innovated Judet plate is its weight, which meets the contemporary trends in construction of rib plates designed for anatomical fixation. The first experience with the innovated plates in flail chest injury confirmed the safety of the procedure for stable osteosynthesis of rib fractures. Adequate stability of the chest wall facilitated an early withdrawal of ventilatory support. Osteosynthesis of rib fractures with innovated plates performed in the first three patient was without complications, including in the postoperative period. DISCUSSION A series of prospective studies prove the correctness of the indications of early rib osteosynthesis in flail chest. Further indications for rib osteosynthesis are postinjury chest deformity, dislocation of rib fracture fragments with a lung injury, and malunion of rib fracture. According to these studies the surgical stabilisation of the chest is a safe and efficient method resulting in pain reduction, decrease of ventilatory support time, and also in reduced morbidity. For rib osteosynthesis anatomical plates, Judet plates and intramedullary plates are used. Our innovation of the Judet plate aimed to improve the technical parameters of the plate. The innovative Judet plate means a significant improvement in technical parameters and stands comparison with the plates of others companies, which are used in the Czech Republic. This is also evidenced by preliminary clinical results. CONCLUSIONS Surgical stabilisation of the flail chest segment is considered to be he method of choice in treating selected patients, leading to the improvement of respiratory function and shortening of the ventilatory support time. The new technical parameters of the plate, including its weight, new fixation clips, locking screws and instruments are the priorities of the innovated Judet plates. The innovation of Judet plates represents an important step towards the extension of indications for surgical stabilisation of the chest. Key words:innovative Judet plates, preclinical study, osteosynthesis of rib fractures.

Nitrification in a completely stirred tank reactor treating the liquid phase of digestate: The way towards rational use of nitrogen

The nitrification of the liquid phase of digestate (LPD) was conducted using a 5L completely stirred tank reactor (CSTR) in two independent periods (P1 - without pH control; P2 - with pH control). The possibility of minimizing nitrogen losses during the application of LPD to the soil as well as during long-term storage or thermal thickening of LPD using nitrification was discussed. Moreover, the feasibility of applying the nitrification of LPD to the production of electron acceptors for biological desulfurization of biogas was assessed. Despite an extremely high average concentration of ammonia and COD in LPD reaching 2470 and 9080mg/L, respectively, nitrification was confirmed immediately after the start-up of the CSTR. N-NO₃^- concentration reached 250mg/L only two days after the start of P1. On the other hand, P1 demonstrated that working without pH control is a risk because of the free nitrous acid (FNA) inhibition towards nitrite oxidizing bacteria (NOB) resulting in massive nitrite accumulation. Up to 30.9mg/L of FNA was present in the reactor during P1, where the NOB started to be inhibited even at 0.15mg/L of FNA. During P2, the control of pH at 7.0 resulted in nitrogen oxidation efficiency reaching 98.3±1.5% and the presence of N-NO₃^- among oxidized nitrogen 99.6±0.4%. The representation of volatile free ammonia within total nitrogen was reduced more than 1000 times comparing with raw LPD under these conditions. Thus, optimum characteristics of the tested system from the point of view of minimizing the nitrogen losses as well as production of electron acceptors for the desulfurization of biogas were gained in this phase of reactor operation. Based on the results of the experiments, potential improvements and modifications of the tested system were suggested.

Changes in Membrane Cholesterol Differentially Influence Preferential and Non-preferential Signaling of the M1 and M3 Muscarinic Acetylcholine Receptors

We have found earlier that changes in membrane cholesterol content have distinct impact on signaling via the M1, M2, or M3 receptors expressed in CHO cells (CHO-M1 through CHO-M3). Now we investigated whether gradual changes in membrane cholesterol exerts differential effects on coupling of the M1 and M3 muscarinic receptors to preferential signaling pathways through Gq/11 and non-preferential Gs G-proteins signaling. Changes in membrane cholesterol resulted in only marginal alterations of antagonist and agonist affinity of the M1 and M3 receptors, and did not influence precoupling of either subtype. Changes in membrane cholesterol did not influence parameters of carbachol-stimulated GTP-γ(35)S binding in CHO-M1 membranes while reduction as well as augmentation of membrane cholesterol lowered the efficacy but increased the potency of carbachol in CHO-M3 membranes. Gradual increase or decrease in membrane cholesterol concentration dependently attenuated agonist-induced inositolphosphates release while only cholesterol depletion increased basal values in both cell lines. Similarly, membrane cholesterol manipulation modified basal and agonist-stimulated cAMP synthesis via Gs in the same way in both cell lines. These results demonstrate that changes in membrane cholesterol concentration differentially impact preferential and non-preferential M1 and M3 receptor signaling. They point to the activated G-protein/effector protein interaction as the main site of action in alterations of M1 receptor-mediated stimulation of second messenger pathways. On the other hand, modifications in agonist-stimulated GTP-γ(35)S binding in CHO-M3 membranes indicate that in this case changes in ligand-activated receptor/G-protein interaction may also play a role.

Importance and prospects for design of selective muscarinic agonists

There are five subtypes of muscarinic receptors that serve various important physiological functions in the central nervous system and the periphery. Mental functions like attention, learning, and memory are attributed to the muscarinic M1 subtype. These functions decline during natural aging and an early deficit is typical for Alzheimer s disease. In addition, stimulation of the M1 receptor increases non-amyloidogenic processing of the amyloid precursor protein and thus prevents accumulation of noxious beta-amyloid fragments. The selectivity of classical muscarinic agonists among receptor subtypes is very low due to the highly conserved nature of the orthosteric binding site among receptor subtypes. Herein we summarize some recent studies with the functionally-selective M1 agonist xanomeline that indicate complex pharmacological profile of this drug that includes interactions with and activation of receptor from both orthosteric and ectopic binding sites, and the time-dependent changes of ligand binding and receptor activation. These findings point to potential profitability of exploitation of ectopic ligands in the search for truly selective muscarinic receptor agonists.

Impairment of muscarinic transmission in transgenic APPswe/PS1dE9 mice

We assessed the integrity of cholinergic neurotransmission in parietal cortex of young adult (7 months) and aged (17 months) transgenic APPswe/PS1dE9 female mice compared to littermate controls. Choline acetyltransferase and acetylcholinesterase activity declined age-dependently in both genotypes, whereas both age- and genotype-dependent decline was found in butyrylcholinesterase activity, vesicular acetylcholine transporter density, muscarinic receptors and carbachol stimulated binding of GTP gamma S in membranes as a functional indicator of muscarinic receptor coupling to G-proteins. Notably, vesicular acetylcholine transporter levels and muscarinic receptor-G-protein coupling were impaired in transgenic mice already at the age of 7 months compared to wild type littermates. Thus, brain amyloid accumulation in this mouse model is accompanied by a serious deterioration of muscarinic transmission already before the mice manifest significant cognitive deficits.

Muscarinic M2 receptors directly activate Gq/11 and Gs G-proteins

Muscarinic M(2) receptors preferentially couple with the G(i/o) class of G-proteins to inhibit cAMP synthesis. However, they can also stimulate net synthesis of cAMP and inositol phosphate (IP) accumulation. We investigated in intact Chinese hamster ovary (CHO) cells expressing human M(2) receptors (CHO-M(2) cells) whether direct interaction of M(2) receptors with G(s) and G(q/11) G-proteins is responsible for the latter effects. Suppression of the G(s)alpha subunit using RNA interference abolished stimulation of cAMP synthesis induced by 1 mM carbachol in both control and pertussis toxin-treated CHO-M(2) cells but had no effect on the inhibition of forskolin-stimulated cAMP synthesis. Carbachol stimulated accumulation of IP with an EC(50) of 79 microM. Removal of the G(q),G(11), or both alpha subunits reduced this response by 78, 54, and 92%, respectively, whereas suppression of the G(s)alpha subunit had no effect. Similar results obtained in CHO cells expressing M(1) receptors that preferentially couple with G(s) and G(q/11) G-proteins confirmed the efficiency of siRNA treatments. Stimulation of M(2) receptors in control and pertussis toxin-treated cells by a series of full agonists with respect to inhibition of adenylyl cyclase displayed different efficacies in stimulating IP accumulation. Carbachol, acetylcholine, and oxotremorine-M [N,N,N-trimethyl-4-(2-oxo-1-pyrolidinyl)-2-butyn-1-ammonium] behaved as full agonists, furmethide (N,N,N-trimethyl-2-furanmethammonium) and methylfurmethide [(5-methyl-2-furyl)methyltrimethylammonium] were partial agonists, and oxotremorine (1-[4-(1-pyrrolidinyl)-2-butynyl]-2-pyrrolidinone) had no effect. Our results provide direct evidence of M(2) receptor coupling with the alpha subunits of G(s) and G(q/11) G-proteins and demonstrate induction of multiple receptor conformational states dependent on both the concentration and the nature of the agonist used.

Regulation of signal transduction at M2 muscarinic receptor

Muscarinic acetylcholine receptors mediate transmission of an extracellular signal represented by released acetylcholine to neuronal or effector cells. There are five subtypes of closely homologous muscarinic receptors which are coupled by means of heterotrimeric G-proteins to a variety of signaling pathways resulting in a multitude of target cell effects. Endogenous agonist acetylcholine does not discriminate among individual subtypes and due to the close homology of the orthosteric binding site the same holds true for most of exogenous agonists. In addition to the classical binding site muscarinic receptors have one or more allosteric binding sites at extracellular domains. Binding of allosteric modulators induces conformational changes in the receptor that result in subtype-specific changes in orthosteric binding site affinity for both muscarinic agonists and antagonists. This overview summarizes our recent experimental effort in investigating certain aspects of M2 muscarinic receptor functioning concerning i) the molecular determinants that contribute to the binding of allosteric modulators, ii) G-protein coupling specificity and subsequent cellular responses and iii) possible functional assays that exploit the unique properties of allosteric modulators for characterization of muscarinic receptor subtypes in intact tissue. A detailed knowledge of allosteric properties of muscarinic receptors is required to permit drug design that will modulate signal transmission strength of specific muscarinic receptor subtypes. Furthermore, allosteric modulation of signal transmission strength is determined by cooperativity rather than concentration of allosteric modulator and thus reduces the danger of overdose.

Modelling the consequences of receptor-G-protein promiscuity

Many G-protein-coupled receptors interact with more than one type of G protein, giving rise to extreme variability in the effects of receptor activation, depending on, for example, receptor density and desensitization, efficacy of agonists, and availability of specific G proteins. This leads to errors in interpretation of data. To facilitate understanding the consequences of receptor-G-protein promiscuity, we use two simplified models to simulate such consequences. Applied to the regulation of adenylyl cyclase and phosphoinositidase, the models predict seemingly paradoxical situations and explain some phenomena that, at first sight, might seem to require the induction of agonist-specific (G-protein-selective) receptor conformations.

Dual effects of muscarinic M2 receptors on the synthesis of cyclic AMP in CHO cells: background and model

It has been observed in several laboratories that muscarinic agonists have dual effects on the synthesis of cyclic AMP in cell lines expressing muscarinic M2 or M4 receptors, producing strong inhibition at low agonist concentrations and lesser inhibition or stimulation at high agonist concentrations. Data obtained on CHO cells (known to express adenylyl cyclases VI and VII) are best interpreted on the assumption that the upward phase of the concentration-response curves reflects simultaneous inhibition of adenylyl cyclase VI via the Gi proteins, with which the M2 and M4 receptors communicate with high affinity, and stimulation of adenyly cyclases VI and VII via the Gs proteins, with which the M2 and M4 receptors communicate with low affinity. A simplified model is described which permits one to predict how the shapes of the concentration-response curves will be affected by changes in the concentration of receptors, the affinities of activated receptors for Gi or Gs proteins, and other parameters.

Dual effects of muscarinic M(2) acetylcholine receptors on the synthesis of cyclic AMP in CHO cells: dependence on time, receptor density and receptor agonists

1. Muscarinic M(2) receptors normally inhibit the production of cyclic AMP via G(i) proteins, but a stimulatory component occurs in their effect at high agonist concentrations, believed to be based on the activation of G(s) proteins. We investigated the conditions which determine the occurrence and extent of the stimulatory component in CHO cells stably expressing muscarinic M(2) receptors. 2. Biphasic concentration-response curves (decline followed by return towards control values) were obtained after 10 min incubation with carbachol, oxotremorine-M, acetylcholine, arecoline and arecaidine propargyl ester, but the upward phase was missing with oxotremorine, methylfurmethide, furmethide and pentylthio-TZTP. Shortening the incubation favoured the occurrence of the stimulatory component. Carbachol (1 mM) and oxotremorine-M (1 mM) brought about net stimulation (above 100% of control) of cyclic AMP synthesis during 2 min incubations. The stimulatory components disappeared after the density of receptors had been lowered with oxyphenonium mustard. 3. All agonists stimulated the synthesis of cyclic AMP in cells pretreated with pertussis toxin. 4. Most differences between agonists regarding the stimulatory component of their effect on cyclic AMP synthesis could be explained by differences in their efficacy and the induced receptor internalization. 5. We propose that the G(s)-mediated stimulatory component of the effect of muscarinic M(2) receptors on cyclic AMP synthesis only occurs if the density of activated receptors is high enough to saturate the G(i) proteins and proportionate to the receptors' low affinity for the G(s) proteins. It tends to be abolished by receptor internalization.

Clozapine interaction with the M2 and M4 subtypes of muscarinic receptors

Available evidence indicates that the antipsychotic drug clozapine acts as a partial agonist at the muscarinic M4 and as an antagonist at the M2 receptors. We wondered whether there is indeed a fundamental difference between its action on these two receptor subtypes, and whether it interacts with their classical or allosteric binding sites. In experiments on Chinese hamster ovary cells stably expressing the M2 or M4 receptors, clozapine inhibited the binding of the specific muscarinic ligand [3H]N-methylscopolamine to either receptor subtype. The affinity of the high-affinity sites for clozapine was diminished by GTP in the way expected for agonists on both the M2 and the M4 receptor subtypes. Arunlakshana-Schild plots of data obtained in saturation binding experiments with [3H]N-methylscopolamine at different concentrations of clozapine were linear with a slope of unity. Clozapine did not alter the time course of [3H]N-methylscopolamine dissociation from muscarinic M2 or M4 receptors. It inhibited the synthesis of cyclic AMP in cells expressing the M4 receptor subtype, but did not measurably inhibit the synthesis of cyclic AMP in cells expressing the M2 receptor subtype. We conclude that clozapine has a high affinity for muscarinic M2 and M4 receptor subtypes, that it associates with the classical and not with the allosteric binding site, and that it acts as a partial agonist on both the M2 and the M4 receptor subtype.