[Kombinovaná lécba mekkotkánového sarkomu v oblasti pánve]. / Kombinovaná lécba mekkotkánového sarkomu v oblasti pánve.

Soft tissue sarcomas (STS) constitute a heterogeneous group of rare malignant tumors of mesenchymal cell origin and they may develop in any part of the body. They can form enormous masses in certain localizations. A case report of a young woman with locally advanced liposarcoma in the pelvic cavity is presented. This example emphasizes the significance of early diagnosis, as only radical surgery can be potentially curative in sarcoma therapy.Key words: advanced pelvic sarcoma multimodal treatment multidisciplinary.

[Anticoagulation and Thrombembolism During Bevacizumab Treatment--To Be Careful or Fearful?]. / Antikoagulacní lécba a trombembolizmus pri lécbe bevacizumabem--opatrnost, ci obavy?

Inhibition of angiogenesis is a valid approach in today's medicine. Besides oncology, it is used in ophthalmology, as well. In oncology, angiogenesis inhibition has become a routine and accessible method. A combination of angiogenesis inhibition and other therapies, including anticoagulation and antiaggregation is common in many cases. Bevacizumab is the most used antiangiogenic agent and has been in use for the longest period of time. A concomitant administration of angiogenesis inhibitors and anticoagulation may be feared by oncologists. From the available literature it is obvious that concomitant administration of bevacizumab and anticoagulation is safe. Also, use of antiaggregation and bevacizumab is safe. The risk of venous and arterial thromboembolism is real during the treatment with bevacizumab. Therefore, concomitant anticoagulation is not only possible but also may be desirable.

[Malignant melanoma treated with radical chemotherapy, resemblance histology of melanoma to soft tissue sarcomas, case report]. / Maligní melanom lécený intenzivní chemoterapií, podobnost histologického obrazu maligního melanomu a nádoru mekkých tkání, kazuistika pacientky.

BACKGROUND: Malignant melanoma is considered to be highly resistant to chemotherapy, radiotherapy, hormonotherapy and standard immunotherapy (interleukin 2, interferon alpha). Radical surgery in the early stages of the disease is still the most efficient method. Since the development of immunotherapy and targeted therapy, the role of palliative chemotherapy for advanced disease may be changing. CASE: A case report regarding 44-year-old woman with extensive tumor of the pectoral wall with contralateral axillary lymphadenopathy is presented. On the basis of imaging methods, histology and immunohistochemistry, the tumor was defined as a sarcoma. Due to PAX7-FKHR fusion gene positivity, rhabdomyosarcoma was the most probable classification. The patient was treated with radical chemotherapy including iphosphamide, vincristine, actinomycin D and doxorubicin with the effect of partial regression of the tumor. This enabled radical surgery of the chest wall tumor. Pathology proved 70% necrosis of the tumor. A contralateral axillary dissection was performed with a finding of two lymph nodes infiltrated with melanoma. The immunohistochemistry markers S100, HMB-45 and Melan A were positive. This resulted in a reclassification of the chest wall tumor to malignant melanoma. The following PET/CT scan was negative. A massive progression of the disease occurred after 5 months. B-RAF mutation leads to a plan of targeted therapy with vemurafenib. CONCLUSION: The case demonstrates the limits of the sensitivity and specificity of immunohistochemical markers of melanoma and the ability of this tumor to imitate various tumors including soft tissue sarcomas. A rare -PAX7-FKHR fusion gene positivity considered specific for rhabdomyosarcoma was found. An extraordinary response to radical chemotherapy with surgical resection led to an improvement of the quality of life and to a prolonged survival comparable with the effect of new targeted treatment for malignant melanoma.

Clinical impact of PAI 1 4G/5G gene polymorphism in colorectal carcinoma patients.

Plasminogen activator ihnibitor (PAI 1) belongs to the plasminogen activator system, which is part of the metastatic cascade and significantly contributes to invasive growth and angiogenesis of malignant tumors. Its plasma level is normally low but 4G/4G homozygotes have higher concentrations of PAI 1. This genotype may be associated with worse prognosis and proximal location of colorectal cancer than 5G/5G homozygotes. In our prospective evaluation we examined plasma level PAI 1 (using photometric microplate method ELISA) pre-surgery and, subsequently, 6-8 weeks later, from 80 patients. For the PAI 1 rs1799889 -675 4G/5G polymorphism test the PCR amplification was used.Analysis of collected data was confirmed that significantly higher plasma levels of PAI 1 were found in patients before starting therapy, which decreased (p=0.004) after initiation of treatment. Patients with higher plasma level PAI 1 before (p=0.013) and after therapy (p=0.004) had significantly shorter survival. We found no relationship between polymorphisms of PAI 1 (-675 4G/5G) in relation to stage, survival or tumor location. PAI 1 is useful as a negative marker of prognosis and could be advantageous when planning adjuvant treatment of patients with colorectal carcinoma. Although opinions on the importance of polymorphisms of PAI 1 in relation to the prognosis are not uniform, it does seem that their role in the prognosis of patients with colorectal cancer is not essential.

[Analysis of prognostic factors in osteosarcoma adult patients, a single institution experience]. / Prognostické faktory konvencního osteosarkomu dospelých pacientu

BACKGROUND: The objective of this report was to estimate long-term outcome and prognostic factors in adult patients with high-grade osteosarcoma. The intended therapeutic strategy included preoperative and/or postoperative chemotherapy as well as surgery of all operable lesions. PATIENTS AND METHODS: We reviewed the clinical data of 36 newly diagnosed adult patients (aged 19-82, average 37.5, median 28.5 years) with high-grade osteosarcoma of the trunk or limbs evaluated by a multidisciplinary team and treated between 1999 and 2010 in Brno. Forty-five percent of patients were over thirty, more than 36% over forty. Thirty-one percent of patients had metastasis at the time of diagnosis. Demographic parameters, tumor-related and treatment-related variables included possible prognostic factors and their impact on response, overall survival (OS) and event-free survival (EFS) were analyzed. RESULTS: All the patients were followed up after treatment. Seventy-three percent of patients were poor responders to chemotherapy. Sixteen patients are alive, and twenty patients died. The survival time ranged from 2 to 177 months (average 45 months, median survival 23 months). The 5-year OS of all patients was 52.4%. OS of patients without metastasis was 68.12%, while 2-year OS with metastasis was 26% only. 5-year EFS was 38.7%. Univariate analysis revealed that the prognosis of adult osteosarcoma patients was significantly related to distant metastasis (p = 0.006), surgical stage (p = 0.00582), serum alkaline phosphatase (ALP) level (p = 0.00841) and serum lactatdehydrogenase (LD) level (p = 0.047). The other analyzed prognostic factors including age had no statistically significant influence on outcome of osteosarcoma in adult patients. CONCLUSION: The prognosis of osteosarcoma in adult patients was significantly correlated to surgical stage, distant metastasis, serum ALP and LD.

[Significance of urokinase and its inhibitors in the invasiveness and metastasing of malignant tumors]. / Význam urokinázy a jejích inhibitoru pro invazi a metastazování zhoubných nádoru

Fibrinolysis is process, which leads to the degradation of fibrin to fibrin monomers. Fibrinolysis helps to regulate hemostasis and prevents the creation of inappropriately large thrombus, which could reduce blood flow to the bloodstream. The main enzyme involved in fibrinolysis is plasmin. Tissue plasminogen activator (tPA) and urokinase (uPA) are agents converting plasminogen into active plasmin, together with urokinase receptor (uPAR) and urokinase inhibitors (PAI 1, PAI 2, PAI 3 and protease nexin) form plasminogen activator system (PAS) which is among others also part of the metastatic cascade and significantly contributes to invasive growth and angiogenesis of malignant tumours. In contrast to tPA that is fundamental in fibrinolysis, uPA plays an essential role in tissue degradation as part of physiological and pathological processes. uPAR is a GPI (glycosylphosphatidylinositol)-anchored protein. The binding of uPA to uPAR results in activation of protein tyrosine kinase, protein kinase C and MAP kinase. At the same time, direct signalling pathway via Jak/STAT cascade utilising signalling transduction of Scr-like protein tyrosine kinase have also been described. uPAR expression is regulated by many growth factors, e.g. EGF, FGF-2 and HGF. It seems that individual PAS factors are involved in the process of rendering malignant tumors invasive. To what degree this influence is essential to specific malignancies, should be answered by further research. In the article the authors present a summary of findings about the interaction of fibrinolysis and tumor process, especially on the effects of urokinase and other activators and their inhibitors in metastasis of malignant tumors. The text contains information on the factors theirs introduction into practice is still the subject of numerous discussions, but in the future, individual PAS factors could play an important role in planning treatment strategies and also could become targets of targeted therapy.

Clinical significance of the plasminogen activator system in relation to grade of tumor and treatment response in colorectal carcinoma patients.

Urokinase (uPA) plays an essential role in the activation of plasminogen to plasmin, and together with its receptor (uPAR), tissue activator (tPA) and urokinase inhibitors (PAI 1, PAI 2, PAI 3 and protease nexin) forms the plasminogen activator system (PAS), a component of metastatic cascade importantly contributing to the invasive growth and angiogenesis of malignant tumours. In our project we examined the expression of uPA, uPAR, PAI 1 and PAI 2 in tumor tissue and we also studied the plasma levels of PAI 1 before and after the initiation of therapy in patients with colorectal carcinoma in relationship to grade of tumor and the treatment response. In our prospective evaluation we included 80 patients treated for adenocarcinoma of the colon and rectum. Analysis of collected data revealed statistically significant evidence of a relationship between the level of PAI 1 in plasma before treatment and grade of the tumor, which increases with tumor grade (p=0.025). We demonstrated that there exists a statistically significant relationship between the expression of PAI 2 (p<0.001) and uPAR (p=0.031) and grade of tumor. We also confirmed a statistically significant relationship between soluble levels of PAI 1 before treatment and therapeutic response (p=0.021). In our group of patients the expression of uPA, uPAR, PAI 1 and 2 in tumor tissue in relation to response to treatment was also assessed. Our results suggest that the greater expression of these parameters in tumor tissue is linked to a worse response to therapy. In conclusion, PAS factors help as a prognostic indicators and could also act as a predictive factor in colorectal carcinoma.

Bile duct malignancies.

Bile duct malignancies include intrahepatic cholangiocarcinoma (ICC), extrahepatic cholangiocarcinoma (ECC), gall bladder carcinoma (GC) and carcinoma of Vater's ampulla (ampulloma). Bile duct neoplasms are rare tumours with overall poor prognosis. The overall incidence affects up to 12.5 per 100,000 persons in the Czech Republic. The mortality rate has risen recently to 9.5 per 100,000 persons. The incidence and mortality have been remarkably stable over the past 3 decades. The survival rate of patients with these tumours is poor, usually not exceeding 12 months. The diagnostic process is complex, uneasy and usually late. Most cases are diagnosed when unresectable, and palliative treatment is the main approach of medical care for these tumours. The treatment remains very challenging. New approaches have not brought much improvement in this field. Standards of palliative care are lacking and quality of life assessments are surprisingly not common. From the scarce data it seems, however, that multimodal individually tailored treatment can prolong patients'survival and improve the health-related quality of life. The care in specialized centres offers methods of surgery, interventional radiology, clinical oncology and high quality supportive care. These methods are discussed in the article in greater detail. Improvements in this field can be sought in new diagnostic methods and new procedures in surgery and interventional radiology. Understanding the tumour biology on the molecular level could shift the strategy to a more successful one, resulting in more cured patients. Further improvements in palliative care can be sought by defining new targets and new drug development. The lack of patients with bile duct neoplasms has been the limiting factor for any improvements. A new design of larger randomized international multicentric clinical trials with prompt data sharing could help to overcome this major problem. Defining standards of palliative care is a necessity. Addressing health-related quality of life could help to assess the real benefit of palliative treatment.

Constitutive inhibitory action of muscarinic receptors on adenylyl cyclase in cardiac membranes and its stereospecific suppression by hyoscyamine.

Muscarinic acetylcholine receptors in the heart have been shown to display agonist-independent spontaneous (constitutive) activity which causes changes in the opening of cardiac ion channels and in the activity of G proteins. We investigated whether an inhibition of the constitutive activity of muscarinic receptors induced by the binding of antagonist brings about a change in the synthesis of cyclic AMP in rat cardiac membranes, and whether the action ofthe antagonist is stereospecific. Atropine and S-(-)-hyoscyamine were indeed found to enhance the forskolin-stimulated synthesis of cyclic AMP in rat cardiac (both atrial and ventricular) membranes by up to 24%. The effect was stereospecific and the potency of R-(+)-hyoscyamine was 30 fold lower than that of the S-(-) enantiomer, confirming that the action of hyoscyamine is receptor-mediated. The effect did not depend on the presence of endogenous acetylcholine in the system used. The results strongly suggest that the adenylyl cyclase in the heart is exposed to continuous mild inhibition by constitutively active muscarinic receptors in the membranes of cardiomyocytes.

Chronic exposure of NG108-15 cells to amyloid beta peptide (A beta(1-42)) abolishes calcium influx via N-type calcium channels.

We investigated whether amyloid-beta-peptide (A beta(1-42)) has an effect on the elevations of the intracellular concentration of Ca2+ ions ([Ca2+]i) induced by depolarizations of NG108-15 cells and on related Ca2+ channels. A beta(1-42) (10-1000 nM) had no immediate effect on depolarization-induced [Ca2+]i elevations. [Ca2+]i increases were slightly diminished in cells grown in the presence of 100 or 1000 nM A beta(1-42). Nifedipine (1 microM) reduced these elevations equally in cells grown in the absence or presence of A beta(1-42). In contrast, the ability of omega-conotoxin GVIA to diminish the depolarization-induced [Ca2+]i responses became lost in cells grown in the presence of 100 nM A beta(1-42). This indicates that the influx of calcium through the N-type Ca2+ channels was compromised by the chronic exposure of cells to a submicromolar concentration of A beta(1-42), presumably because of impairement of their function or diminished expression. This may be important in the pathogeny of Alzheimer's dementia in view of the pivotal role of N-type Ca2+ channels in neurotransmitter release.

Changes of cooperativity between N-methylscopolamine and allosteric modulators alcuronium and gallamine induced by mutations of external loops of muscarinic M(3) receptors.

To clarify the involvement of specific domains of muscarinic receptors in the action of allosteric modulators, muscarinic M(3) receptors (on which allosteric interactions are weak) were genetically modified to become more similar to M(2) receptors (on which allosteric interactions are strong) and were expressed in COS-7 cells. Affinity for allosteric modulator gallamine was enhanced 25- to 50-fold by modifications of the third external loop (o3) and the negative effect of gallamine on the affinity for classical antagonist N-[(3)H]methylscopolamine ([(3)H]NMS) was augmented. Affinity for alcuronium became 3-fold higher after the o3 loop of M(3) receptors was made identical with the o3 loop of M(2) receptors, and alcuronium acquired positive influence on the affinity for [(3)H]NMS. This is the first instance of inducing positive cooperativity on muscarinic receptors by genetic manipulation. Transferring whole o2 loop from M(2) to M(3) receptors substantially enhanced affinities for gallamine and alcuronium without augmenting their negative action on [(3)H]NMS binding. In contrast, effects of simply adding two negative charges into the o2 loop of M(3) receptors were small. Removal of Arg from o1 loop abolished the negative effect of gallamine but not of alcuronium on [(3)H]NMS binding at equilibrium. Data point to an important role of o3 loop in the mechanism of the positive and negative cooperativity between [(3)H]NMS and alcuronium and gallamine, respectively, and in the binding of both modulators to M(2) receptors and reveal independence between mutation-induced changes in the affinity for a modulator and in the magnitude and direction of the allosteric effect of the modulator.

Differentiation of NG108-15 cells induced by the combined presence of dbcAMP and dexamethasone brings about the expression of N and P/Q types of calcium channels and the inhibitory influence of muscarinic receptors on calcium influx.

Differentiation of cholinergic cell line NG108-15 induced by a combination of dibutyryl cyclic AMP (dbcAMP) and dexamethasone enhances the cholinergic phenotype of the cells more than that induced by either agent alone. We investigated the effect of treatment with dbcAMP and dexamethasone on potassium depolarization-evoked influx of calcium and its regulation by the muscarinic agonist carbachol. Depolarization of control cells and of cells differentiated in the presence of dbcAMP or dexamethasone alone, or in the combined presence of dbcAMP and dexamethasone induced, respectively, 2.2-, 4.3-, 2.7- and 10.7-fold increases of the resting [Ca(2+)](i). Dexamethasone alone and the combination of dbcAMP and dexamethasone augmented the number of muscarinic receptors by 25 and 40%, respectively. Inhibitors of N (omega-conotoxin GVIA) or P/Q (omega-agatoxin TK) calcium channels had no effect on Ca(2+) influx in control cells, whereas in cells differentiated in the combined presence of dbcAMP and dexamethasone they significantly diminished the influx of Ca(2+) by 20 and 5%, respectively. Carbachol attenuated calcium influx in differentiated cells in an atropine-insensitive manner if it was present during stimulation. This effect of carbachol was probably due to an open-channel block of L type channels. In the presence of nifedipine, carbachol attenuated the influx of Ca(2+) into cells differentiated with dbcAMP and dexamethasone by 20% in an atropine-sensitive way. Data show that differentiation of NG108-15 cells by dbcAMP and dexamethasone promotes the expression of functional nifedipine-insensitive N and P/Q types of Ca(2+) channels and that the nifedipine-insensitive calcium influx becomes subject to inhibitory regulation by muscarinic receptors.

Interactions between allosteric modulators and 4-DAMP and other antagonists at muscarinic receptors: potential significance of the distance between the N and carboxyl C atoms in the molecules of antagonists.

Allosteric enhancement of the affinity of muscarinic receptors for their ligands offers a new way to influence cholinergic neurotransmission. The structure of the allosteric binding domain(s) and the features of agonists, antagonists and modulators which determine the occurrence of either positive or negative cooperativity require clarification. We tested interactions between allosteric modulators alcuronium, strychnine and brucine and eight antagonists at muscarinic receptors expressed in CHO cells. In experiments with unlabeled antagonists, all three modulators enhanced the affinity for 4-diphenylacetoxy-N-dimethylpiperidinium (4-DAMP) at the M2 receptors, and strychnine did so also at the M4 receptors. Positive interactions were also observed between alcuronium and L-hyoscyamine (M2) and scopolamine (M2), between strychnine and butylscopolamine (M4), L-hyoscyamine (M2 and M4) and scopolamine (M4), and between brucine and scopolamine (M2). Positive effects of alcuronium, strychnine and brucine on the affinity of the M2 receptors for 4-DAMP have been confirmed by direct measurements of the binding of [3H]-4-DAMP. A comparison of molecular models of several antagonists which are esters revealed that antagonists in which the distance between the N and the carboxyl C atoms corresponds to five chemical bonds are more likely to display positive cooperativity with alcuronium at the M2 receptors than the antagonists in which the N-carboxyl C distance corresponds to four chemical bonds.

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.

Evidence for a tandem two-site model of ligand binding to muscarinic acetylcholine receptors.

After short preincubations with N-[(3)H]methylscopolamine ([(3)H]NMS) or R(-)-[(3)H]quinuclidinyl benzilate ([(3)H]QNB), radioligand dissociation from muscarinic M(1) receptors in Chinese hamster ovary cell membranes was fast, monoexponential, and independent of the concentration of unlabeled NMS or QNB added to reveal dissociation. After long preincubations, the dissociation was slow, not monoexponential, and inversely related to the concentration of the unlabeled ligand. Apparently, the unlabeled ligand becomes able to associate with the receptor simultaneously with the already bound radioligand if the preincubation lasts for a long period, and to hinder radioligand dissociation. When the membranes were preincubated with [(3)H]NMS and then exposed to benzilylcholine mustard (covalently binding specific ligand), [(3)H]NMS dissociation was blocked in wild-type receptors, but not in mutated (D99N) M(1) receptors. Covalently binding [(3)H]propylbenzilylcholine mustard detected substantially more binding sites than [(3)H]NMS. The observations support a model in which the receptor binding domain has two tandemly arranged subsites for classical ligands, a peripheral one and a central one. Ligands bind to the peripheral subsite first (binding with lower affinity) and translocate to the central subsite (binding with higher affinity). The peripheral subsite of M(1) receptors may include Asp-99. Experimental data on [(3)H]NMS and [(3)H]QNB association and dissociation perfectly agree with the predictions of the tandem two-site model.

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.

Subtype-selective inhibition of [methyl-3H]-N-methylscopolamine binding to muscarinic receptors by alpha-truxillic acid esters.

Seven esters of alpha-truxillic acid have been synthesized: bis-3-piperidylpropyl ester and its quaternary bis-N-ethyl derivative, bis-N-diethylaminopropyl ester and its quaternary bis-N-methyl derivative, and bis-4-piperidylbutyl ester and its quaternary bis-N-methyl and bis-N-ethyl derivatives. All esters inhibited the specific binding of muscarinic receptor antagonist [methyl-3H]-N-methylscopolamine ([3H]-NMS) to muscarinic receptors in membranes of CHO cell lines stably expressing the human gene for the M1, M2, M3 or M4 subtype of muscarinic receptors. All esters displayed the highest potency at the M2 and the lowest potency at the M3 receptor subtype. In experiments performed on the M2 muscarinic receptor subtype, the affinity between the receptors and the esters was greatly increased when the concentration of ions was diminished. The highest affinities were found for the tertiary bis-3-piperidylpropyl and bis-4-piperidylbutyl aminoesters (equilibrium dissociation constants of 52 and 179 pM, respectively, in the low ionic strength medium). All investigated esters slowed down the dissociation of [3H]-NMS from the M2 muscarinic receptor subtype. [3H]-NMS dissociation from the M1, M3 and M4 muscarinic receptor subtypes was investigated in experiments with the bis-4-piperidylbutyl aminoester and also found to be decelerated. It is concluded that the esters of alpha-truxillic acid act as M2-selective allosteric modulators of muscarinic receptors and that, by their potency, the tertiary bis-3-piperidylpropyl and bis-4-piperidylbutyl aminoesters surpass the other known allosteric modulators of these receptors.

Calcium channels involved in the inhibition of acetylcholine release by presynaptic muscarinic receptors in rat striatum.

1. The mechanism of the inhibitory action of presynaptic muscarinic receptors on the release of acetylcholine from striatal cholinergic neurons is not known. We investigated how the electrically stimulated release of [3H]-acetylcholine from superfused rat striatal slices and its inhibition by carbachol are affected by specific inhibitors of voltage-operated calcium channels of the L-type (nifedipine), N-type (omega-conotoxin GVIA) and P/Q-type (omega-agatoxin IVA). 2. The evoked release of [3H]-acetylcholine was not diminished by nifedipine but was lowered by omega-conotoxin GVIA and by omega-agatoxin IVA, indicating that both the N- and the P/Q-type (but not the L-type) channels are involved in the release. The N-type channels were responsible for approximately two thirds of the release. The release was >97% blocked when both omega-toxins acted together. 3. The inhibition of [3H]-acetylcholine release by carbachol was not substantially affected by the blockade of the L- or P/Q-type channels. It was diminished but not eliminated by the blockade of the N-type channels. 4. In experiments on slices in which cholinesterases had been inhibited by paraoxon, inhibition of [3H]-acetylcholine release by endogenous acetylcholine accumulating in the tissue could be demonstrated by the enhancement of the release after the addition of atropine. The inhibition was higher in slices with functional N-type than with functional P/Q-type channels. 5. We conclude that both the N- and the P/Q-type calcium channels contribute to the stimulation-evoked release of acetylcholine in rat striatum, that the quantitative contribution of the N-type channels is higher, and that the inhibitory muscarinic receptors are more closely coupled with the N-type than with the P/Q-type calcium channels.

Effects of an agonist, allosteric modulator, and antagonist on guanosine-gamma-[35S]thiotriphosphate binding to liposomes with varying muscarinic receptor/Go protein stoichiometry.

We investigated whether alcuronium, an allosteric modulator of muscarinic acetylcholine receptors, can induce receptor-mediated activation of Go proteins in liposomal membranes incorporating purified M2 receptors and Go proteins and whether its action is affected by the receptor/Go protein (R/Go) ratio. The binding of guanosine-gamma-[35S]thiotriphosphate ([35S]GTPgammaS) served as the indicator of G protein activation. It was stimulated by empty receptors at high receptor densities, and the dose-response curve was shifted to the left by the agonist carbachol and to the right by the antagonist atropine. At an R/Go ratio of 300:100, the rate of [35S]GTPgammaS binding was the same in the presence or absence of 0. 1 mM carbachol. Alcuronium increased the binding of [35S]GTPgammaS at R/Go ratios of <3:100 and diminished it at R/Go ratios of >10:100, similar to previous observations on intact cells expressing muscarinic receptors at different densities. The apparent biphasicity of alcuronium action indicates that the allosteric modulator has at least two effects on muscarinic receptor/G protein interaction but its mechanistic basis is unclear. The "active state" of muscarinic receptors induced by alcuronium probably is different from that induced by carbachol. Changes in the densities of receptors and Go proteins had little effect on the kinetics of [35S]GTPgammaS binding and on receptor affinity for carbachol, provided the R/Go ratio was kept constant. This suggests that the receptors and G proteins are located in microdomains in which their concentrations remain constant, despite variations in the amounts of lipidic membranes in the system.