[Cutaneous foreign body granulomas following cervico-facial arterial embolization: Three cases]

BACKGROUND

Foreign body granuloma is an inflammatory tissue reaction to exogenous material. Classically it appears on the face after aesthetic procedures. Herein we report for the first time three cases of facial granulomatous reactions to microbeads after arterial cervico-facial embolization.

PATIENTS AND METHODS

Three patients underwent embolization of the facial arteries using Embogold^® microbeads in a setting of epistaxis or tumoral hemostasis. Within 10 to 45 days painful, inflammatory, subcutaneous nodules appeared on the homolateral side of the face. Histological samples showed an inflammatory response with giant cells as well as the presence of microbeads in the skin. A favorable outcome was achieved with colchicine in one patient and with surgery in another; the third patient was lost to follow-up.

DISCUSSION

The embolizing microspheres produced a local inflammatory reaction, with destruction of the vascular wall and bead migration to facial tissue leading to a granulomatous reaction. The occurrence of three cases within a period of few weeks, with several different operators and batches of products, is surprising considering the long-standing use of the product. There was no common comorbidity in the patients and no suggestion of trauma. Retrospective analysis of the product batches was normal. Gold staining could play a role in severe inflammatory response to Embogold^® particles.

CONCLUSION

These three cases illustrate the value of discussing potential foreign body granulomatous reaction in cases of facial nodules following cervico-facial embolization. Colchicine may offer a valuable therapeutic alternative.

Update on PARP Inhibitors in Breast Cancer

OPINION STATEMENT

The single agent activity of PARP inhibitors (PARPi) in germline BRCA mutated (gBRCAm) breast and ovarian cancer suggests untapped potential for this new class of drug in breast cancer. The US Food and Drug Administration has approved three PARPi (olaparib, rucaparib, and niraparib) so far to treat certain ovarian cancers, including those with gBRCAm and olaparib for treatment of gBRCAm breast cancers. Several PARPi are now under clinical development for breast cancer in the various treatment settings. Recently, two phase III trials of olaparib (OlympiaD) and talazoparib (EMBRACA) demonstrated 3-month progression-free survival improvement with PARPi compared to physician's choice single agent chemotherapy in metastatic gBRCAm breast cancer. To date, PARPi seems less efficacious in metastatic breast cancer patients than those with BRCA mutated platinum-sensitive recurrent ovarian cancer, perhaps reflecting the biologic heterogeneity and low somatic BRCA mutation rate in breast cancer. The use of PARPi is gradually evolving, including combination strategies with chemotherapy, targeted agents, radiotherapy, or immunotherapy in women with and without gBRCAm. The role of predictive biomarkers, including molecular signatures and homologous recombination repair deficiency scores based on loss of heterozygosity and other structural genomic aberrations, will be crucial to identify a subgroup of patients who may have benefit from PARPi. An improved understanding of the mechanisms underlying PARPi clinical resistance will also be important to enable the development of new approaches to increase efficacy. This is a field rich in opportunity, and the coming years should see a better understanding of which breast cancer patients we should treat with PARPi and where these agents should come in over the course of treatment.

Modulation of the conformational state of the SV2A protein by an allosteric mechanism as evidenced by ligand binding assays

BACKGROUND AND PURPOSE

Synaptic vesicle protein 2A (SV2A) is the specific binding site of the anti-epileptic drug levetiracetam (LEV) and its higher affinity analogue UCB30889. Moreover, the protein has been well validated as a target for anticonvulsant therapy. Here, we report the identification of UCB1244283 acting as a SV2A positive allosteric modulator of UCB30889.

EXPERIMENTAL APPROACH

UCB1244283 was characterized in vitro using radioligand binding assays with [(3)H]UCB30889 on recombinant SV2A expressed in HEK cells and on rat cortex. In vivo, the compound was tested in sound-sensitive mice.

KEY RESULTS

Saturation binding experiments in the presence of UCB1244283 demonstrated a fivefold increase in the affinity of [(3)H]UCB30889 for human recombinant SV2A, combined with a twofold increase of the total number of binding sites. Similar results were obtained on rat cortex. In competition binding experiments, UCB1244283 potentiated the affinity of UCB30889 while the affinity of LEV remained unchanged. UCB1244283 significantly slowed down both the association and dissociation kinetics of [(3)H]UCB30889. Following i.c.v. administration in sound-sensitive mice, UCB1244283 showed a clear protective effect against both tonic and clonic convulsions.

CONCLUSIONS AND IMPLICATIONS

These results indicate that UCB1244283 can modulate the conformation of SV2A, thereby inducing a higher affinity state for UCB30889. Our results also suggest that the conformation of SV2A per se might be an important determinant of its functioning, especially during epileptic seizures. Therefore, agents that act on the conformation of SV2A might hold great potential in the search for new SV2A-based anticonvulsant therapies.

Peripheral and central H1 histamine receptor occupancy by levocetirizine, a non-sedating antihistamine; a time course study in the guinea pig

BACKGROUND AND PURPOSE

The H(1) receptor occupancy (H1RO) in brain is an indicator of central side effects of antihistamines. Here, we determined the kinetics of central and peripheral H1RO by levocetirizine in relation to its brain and plasma concentration, and investigated the role of the blood-brain barrier in any delay in brain H1RO.

EXPERIMENTAL APPROACH

Concentration-time profiles in plasma and brain were obtained after 0.1 and 1 mg kg(-1) oral doses of levocetirizine in guinea pigs. H1RO in brain was measured ex vivo using [3H]-mepyramine and, in the periphery, by measuring the degree of inhibition of histamine-induced contractions of isolated guinea pig ileum.

KEY RESULTS

The concentration-time profile of levocetirizine indicated lower levels (partition coefficient, K(p)=0.06-0.08), higher t(max) (2-4 h vs 1-1.5 h) and longer terminal half-life (4-5.6 h vs 2.1-2.8 h) in brain than plasma. The H1RO at 0.1 and 1 mg kg(-1) were 75% and 97%, respectively, at 1 hr in the periphery and, in the brain, were <20% and 28-67% respectively, at all time points studied. Brain H1RO vs plasma concentrations profile showed a delay, but not when compared to brain concentrations.

CONCLUSIONS AND IMPLICATIONS

This study demonstrates an effective peripheral antihistamine effect of levocetirizine without central adverse effects at the dose close to human therapeutic dose. The slow increase in H1RO in the brain with time was caused by slow blood-brain barrier transport of levocetirizine. This demonstrates the importance of measuring time course of brain H1RO in relation to brain concentrations of drugs.

The use of IRES-based bicistronic vectors allows the stable expression of recombinant G-protein coupled receptors such as NPY5 and histamine 4

Stable expression of G protein coupled receptors in cell lines is a crucial tool for the characterization of the molecular pharmacology of receptors and the screening for new antagonists. However, in some instances, many difficulties have been encountered to obtain stable cell lines expressing functional receptors. Here, we addressed the question of vector optimization to establish cell lines expressing the human neuropeptide Y receptor 5 (NPY5-R) or histamine receptor 4 (HH4R). We have compared bicistronic vectors containing viral or cellular internal ribosome entry sites (IRES), co-expressing the receptor and the neomycine resistance gene from a single mRNA, to a bigenic vector containing two distinct promoters upstream each different genes. This study is the first one to validate the use of three cellular IRESs for long-term transgene expression. Our results demonstrate for both NPY5-R and HH4R that the bicistronic vectors with EMCV, VEGF, FGF1A or FGF2 IRES provide clones expressing functional receptors with yields between 25% and 100%. In contrast, the bigenic vector provided no functional clones, related to a low expression of NPY5R mRNA. The cell lines expressing active receptor were stable after more than 50 passages. These data indicate that IRES-based bicistronic vectors are particularly appropriate to establish cell clones expressing active G-coupled protein receptors with a high yield. In the case of NPY5, it was a new way to produce such a stable cell line. Furthermore, the characteristics-presented herein-of this receptor pharmacological property are perfectly in line with those reported in the literature.

Histamine H1 receptor occupancy and pharmacodynamics of second generation H1-antihistamines

The predictive efficacy of drugs in humans is frequently estimated from both a high affinity for their receptor as measured in vitro and a long plasmatic half-life. This is grossly misleading since one key parameter is missing: drug concentration at the receptor site in vivo. As a case study we compared the efficacies of three H(1) antihistamines in inhibiting histamine-induced wheal and flare in humans at two different time points with the above mentioned parameters. It is concluded that estimating in vivo receptor occupancy, which takes into account both the affinity of the drug for the receptor and its free plasma concentration, is a far better predictor for human pharmacodynamics and hence antihistamine potency, than considering in vitro affinity and plasmatic half-life only.

Experimental production of gastric dilation and its association with osmoregulatory stress and biogenic amines in chinook salmon, Oncorhynchus tshawytscha (Walbaum)

Chinook salmon smolt in fresh water fed a commercial diet known to produce minimal gastric dilation and air sacculitis (GDAS) were randomly assigned to four experimental tanks with flow-through sea water. All four groups were acclimatized to sea water for 3 weeks and fed a diet of minced fresh seafood. After 3 weeks the groups were fed either; seafood as before, a different commercial pelleted diet associated with the development of GDAS on farms, or either diet supplemented with 500 mg L(-1) putrescine, 300 mg L(-1) cadaverine and 250 mg L(-1) tyramine. Gastric dilation was produced in fish fed the commercial diet for 1 month but not by feeding a diet of minced seafood. The addition of putrescine, cadaverine and tyramine to either diet had no significant effect on the development of gastric dilation. Fish fed the commercial diet had significantly (P < 0.0001) wider weight-adjusted stomach widths, less prominent longitudinal stomach folds (P < 0.0001) and lower (P < 0.0001) stomach-width ratios than fish fed the fresh seafood diet. There was no significant difference in serum osmolality or sodium concentration between fish from groups with or without gastric dilation or fed biogenic amines.

Discovery of orally bioavailable NK1 receptor antagonists

Benzyloxyphenethylpiperazines are a new class of high affinity NK1 receptor antagonists. Oral bioavailability and selectivity can be fine tuned by the nature of the substituents on the basic nitrogen atom. Addition of substituents with a carboxylic acid group led to very selective and orally active NK1 antagonists free of interaction with L-type calcium channels.

A new series of M3 muscarinic antagonists based on the 4-amino-piperidine scaffold

A series of 4-amino-piperidine containing molecules have been synthesized and structure-affinity relationship toward the M3-muscarinic receptor has been investigated. Chemical modulations provided molecules with K(i) for the human M3-R up to 1 nM with variable selectivity (3- to 40-fold) over the human M2-R. Compounds 2 (pA(2)=8.3, 8.6) demonstrates in vitro on guinea pig bladder and ileal strips potent anticholinergic properties and tissue selectivity.

[Is it necessary to operate quickly in patients with significant left main coronary stenosis?]

Although coronary bypass surgery is performed rapidly in the majority of cases of left main coronary stenosis to prevent cardiovascular complications, there is no reported consensus in the literature about the ideal interval between diagnostic coronary angiography and surgery. The aim of this multicenter study was to make an inventory of the serious vascular cardiovascular events which occurred between coronary angiography and surgery to determine possible predictive factors for complications and thereby identify a high risk subgroup requiring immediate revascularisation. The population comprised 283 patients with significant left main coronary disease, out of a total of 8,205 patients who underwent coronary angiography in the university hospitals of Angers, Brest, Nantes, Poitiers and Rennes. A surgical indication was retained in 216 patients. The choice of the operation date depended on clinical data in the presence of an acute coronary syndrome, patients remaining in the intensive care unit and undergoing revascularisation rapidly. Serious cardiac events (death, myocardial infarction, refractory unstable angina and left ventricular failure) occurring while waiting for surgery were rare, observed in only 6.5% of patients. Recent myocardial infarction and, to a lesser degree, unstable angina and/or left ventricular systolic dysfunction, were predictive of serious cardiac complications before surgery. The severity of the left main coronary disease and the association of right coronary disease did not increase the risk of serious cardiac events in the preoperative period. The low incidence of complications demonstrates that this strategy enables patients to wait for surgery with an acceptable risk without having to operate all patients with left main coronary disease as an emergency.

Northern exposure

The operators of Alaska's Alyeska pipeline have often claimed an outstanding record in preventing accidents and environmental damage. This article highlights that, contrary to these claims, Alyeska's operations have brought with them a life-threatening gamble with Alaska's fragile environment. The authors document how the operators of Alyeska have misled the public about the company's real safety record, while at the same time preventing employees from speaking out. As the oil companies consolidate globally, territorial entities such as Alaska can literally assume the character of an oil province.

Community integration and life satisfaction after traumatic brain injury: long-term findings

OBJECTIVE

This study examines the relationship of the degree of community integration to the life satisfaction of persons with traumatic brain injury (TBI).

METHOD

The responses to two self-administered questionnaires measuring aspects of community integration and life satisfaction were studied for 30 persons with TBI who were 26 to 60 years of age.

RESULTS

A significant relationship (rho = .37, p < .05) was found between life satisfaction and social integration (a component of community integration). No significant association was found between the total community integration score and life satisfaction.

CONCLUSION

The results suggest the need for rehabilitation programs to provide long-term assistance with community-based social integration as well as more effective treatment strategies to develop these skills in persons with TBI.

The novel alpha 2-adrenoceptor agonist [3H]mivazerol binds to non-adrenergic binding sites in human striatum membranes that are distinct from imidazoline receptors

The alpha 2 adrenergic agonist [3H]mivazerol labelled two populations of binding sites in membranes from the human striatum. Forty per cent of the sites labelled by 3 nM [3H]mivazerol corresponded to alpha 2 adrenergic receptors as they displayed a high affinity for (-)-adrenaline and for rauwolscine. The remaining binding was displaced by mivazerol with a pIC50 of 6.5 +/- 0.1. These sites displayed higher affinity for dexmedetomidine (pIC50 = 7.1 +/- 0.1), but much lower affinity for clonidine (pIC50 < 5.0) and for idazoxan (pIC50 = 5.1 +/- 0.1). Mivazerol also showed low affinity for the [3H]clonidine-labelled I1 imidazoline receptors and for the [3H]idazoxan-labelled I2 receptors (pIC50 = 5.1 and 3.9, respectively). These results suggest that the non-adrenergic [3H]mivazerol binding sites are distinct from the imidazoline receptors in the human striatum.

The effect of anticipatory discharge orders on length of hospital stay in staff pediatric patients

Effective discharge planning should serve to reduce length of stay (LOS) and lower readmission rates. A combined prospective/retrospective study was undertaken to assess the effectiveness of anticipated discharge order forms in decreasing LOS for staff pediatric patients. Resident physicians provided advance notice of the planned discharge date to nursing staff and patient family members. Patient selection was random, and the data were collected prospectively. These subjects were matched with patients for whom the order form was not used, and the data was collected retrospectively. Matching variables included: diagnosis, age, gender, race, and method of payment. There were 103 matched pairs. LOS was collapsed into low and high categories. There was a significant difference when comparing subject groups (chi 2 = 8.5; P = 0.005). Whereas only 14% of experimental patients were categorized as high LOS, 32% of control patients were classified as such. Physician prediction of discharge date helped decrease patient LOS.

Longitudinal Assessment of Stroke Survivors' Handicap

Proxy agreement for telephone administration of the Craig Handicap Assessment and Reporting Technique (CHART) to community-living individuals 18 months poststroke and their caregivers was assessed and compared to in-person interview of the same sample 1 year earlier. Proxy agreement was adequate for a summary score and for all but one of the dimensions (social integration), replicating prior findings. Physical independence, mobility, and occupation dimensions were intercorrelated. Scores for these dimensions at 6 months poststroke predicted later scores. The study contributes to the validity of the CHART, especially the physical independence, mobility, and occupation dimensions.

Telephone and in-person proxy agreement between stroke patients and caregivers for the functional independence measure

This study examined patient/proxy agreement for telephone administration of the Functional Independence Measure (FIM) to a sample of 25 community-living stroke patients 18 mo post-stroke and their caregivers. Patients had all received in-patient rehabilitation for stroke. Because use of the FIM is increasing for follow-up purposes, it is important to document whether it is appropriate to administer a telephone version to proxy caregivers in situations in which patients cannot answer for themselves. Proxy agreement results were then compared with those obtained for in-person administration of the FIM to the same sample 1 yr earlier. Overall, proxy agreement for telephone administration was excellent for total scores (intraclass correlation was 0.91) and the physical dimension (0.94) and lower for the cognitive dimension (0.52), closely paralleling results obtained for the earlier in-person administration. Reasons for lower agreement on the cognitive dimension are discussed.

[Mutagenesis of the human histamine H1 receptor and design of new antihistamine agents]

The binding cavity of histamine and histamine antagonists is explored using site directed mutagenesis of the human histamine H1 receptor and the amino acids involved in ligand binding are identified. Whereas Asp107 and Phe199 are important for both agonists and antagonists, two additional amino acids (Asn198 and Trp103) are required for efficient histamine binding. The binding site of antagonists is best defined as resulting from a strong ionic bond to Asp107, an orthogonal interaction between one of the aromatic rings with Phe199, and probably a hydrophobic interaction between the second aromatic ring and the lipophilic amino acids of the upper part of TMIV and TMV. This is consistent with structure-activity data of most described antagonists.

The novel antiepileptic drug levetiracetam (ucb L059) appears to act via a specific binding site in CNS membranes

Levetiracetam ((S)-alpha-ethyl-2-oxo-pyrrolidine acetamide, ucb L059) is a novel potential antiepileptic agent presently in clinical development with unknown mechanism of action. The finding that its anticonvulsant activity is highly stereoselective (Gower et al., 1992) led us to investigate the presence of specific binding sites for [3H]levetiracetam in rat central nervous system (CNS). Binding assays, performed on crude membranes, revealed the existence of a reversible, saturable and stereoselective specific binding site. Results obtained in hippocampal membranes suggest that [3H]levetiracetam labels a single class of binding sites (nH = 0.92 +/- 0.06) with modest affinity (Kd = 780 +/- 115 nM) and with a high binding capacity (Bmax = 9.1 +/- 1.2 pmol/mg protein). Similar Kd and Bmax values were obtained in other brain regions (cortex, cerebellum and striatum). ucb L060, the (R) enantiomer of levetiracetam, displayed about 1000 times less affinity for these sites. The binding of [3H]levetiracetam is confined to the synaptic plasma membranes in the central nervous system since no specific binding was observed in a range of peripheral tissues including heart, kidneys, spleen, pancreas, adrenals, lungs and liver. The commonly used antiepileptic drugs carbamazepine, phenytoin, valproate, phenobarbital and clonazepam, as well as the convulsant agent t-butylbicyclophosphorothionate (TBPS), picrotoxin and bicuculline did not displace [3H]levetiracetam binding. However, ethosuximide (pKi = 3.5 +/- 0.1), pentobarbital (pKi = 3.8 +/- 0.1), pentylenetetrazole (pKi = 4.1 +/- 0.1) and bemegride (pKi = 5.0 +/- 0.1) competed with [3H]levetiracetam with pKi values comparable to active drug concentrations observed in vivo. Structurally related compounds, including piracetam and aniracetam, also displaced [3H]levetiracetam binding. (S) Stereoisomer homologues of levetiracetam demonstrated a rank order of affinity for [3H]levetiracetam binding in correlation with their anticonvulsant activity in the audiogenic mouse test (r2 = 0.84, n = 12, P < 0.0001). These results support a possible role of this binding site in the anticonvulsant activity of levetiracetam and substantiate the singular pharmacological profile of this compound. This site remains however to be further characterised.

Sebaceous carcinoma

Sebaceous carcinoma is a rare, aggressive, malignant tumor derived from the adnexal epithelium of sebaceous glands. It may arise in ocular or extraocular sites and exhibits such a variety of histologic growth patterns and diverse clinical presentations that the diagnosis is often delayed for months to years. We discuss incidence as well as clinical, histologic, diagnostic, prognostic, and management issues of this aggressive neoplasm.

The role of dermabrasion and chemical peels in the treatment of patients with xeroderma pigmentosum

We describe our experience with two patients with xeroderma pigmentosum who underwent periodic trichloroacetic acid chemical peels. One also received a full-face dermabrasion. The effect of chemical peeling was more transient than dermabrasion but was associated with less morbidity. Both chemical peeling and dermabrasion provided a prophylactic effect against the development of skin malignancies; the latter had a more pronounced effect.

Pilot histologic and ultrastructural study of the effects of medium-depth chemical facial peels on dermal collagen in patients with actinically damaged skin

BACKGROUND

Chemical peels are employed for a variety of benign and premalignant skin disorders.

OBJECTIVE

We compared clinical and histologic features with ultrastructural changes that occur after medium-depth chemical facial peel.

METHODS

Three men with actinically damaged facial skin underwent a single 35% trichloroacetic acid peel. Biopsy specimens were taken before the peel, and 2 weeks and 3 months after the peel, for histologic examination, electron microscopy, and gel electrophoresis to assess total collagen type I content.

RESULTS

Clinical resolution of actinic damage corresponded with restoration of epidermal polarity. Collagen type I was markedly increased after the peel. Characteristic ultrastructural features of skin after peeling include markedly decreased epidermal intracytoplasmic vacuoles, decreased elastic fibers, and increased activated fibroblasts.

CONCLUSION

Electron microscopic studies after a medium-depth chemical peel of photodamaged skin reveal more profound changes than those seen histologically.

Pharmacological and functional characterisation of the wild-type and site-directed mutants of the human H1 histamine receptor stably expressed in CHO cells

A cDNA clone for the human histamine H1 receptor was isolated from a lung cDNA library and stably expressed in CHO cells. The recombinant receptor protein present in the cell membranes, displayed the functional and binding characteristics of histamine H1 receptors. Mutation of Ser155 to Ala in the fourth transmembrane domain did not significantly change the affinity of the receptor for histamine and H1 antagonists. However, mutation of the fifth transmembrane Asn198 to Ala resulted in a dramatic decrease of the affinity for histamine binding, and for the histamine-induced polyphosphoinositides breakdown, whereas the affinity towards antagonists was not significantly modified. In addition, mutation of another fifth transmembrane amino acid, Thr194 to Ala also diminished, but to a lesser extent, the affinity for histamine. These data led us to propose a molecular model for histamine interaction with the human H1 receptor. In this model, the amide moiety of Asn198 and the hydroxyl group of Thr194 are involved in hydrogen bonding with the nitrogen atoms of the imidazole ring of histamine. Moreover, mutation of Thr194 to Ala demonstrated that this residue is responsible for the discrimination between enantiomers of cetirizine.

Stable expression of human H1-histamine-receptor cDNA in Chinese hamster ovary cells. Pharmacological characterisation of the protein, tissue distribution of messenger RNA and chromosomal localisation of the gene

A cDNA clone for the histamine H1 receptor was isolated from a human lung cDNA library; it encoded a protein of 487 amino acids which showed characteristic features of G-protein-coupled receptors. The percentages of identity of the deduced amino acid sequence with bovine, rat and guinea pig H1 histamine receptors were 82.6%, 79.4% and 73.3%, respectively, whereas these percentages decreased to 74.6%, 66% and 56.7% for the amino acid sequence of the third intracellular loop. The human H1-receptor cDNA was transfected into Chinese hamster ovary cells (CHO) via an eukaryotic expression vector; the receptor protein present on cell membranes specifically bound [3H]mepyramine with a Kd of 3.7 nM. The binding was displaced by H1-histamine-receptor antagonists and histamine. Northern blot analysis indicated the presence of two histamine H1 receptor mRNAs of 3.5 kb and 4.1 kb in various human tissues and an additional mRNA of 4.8 kb restricted to the human brain. Finally, by means of somatic cell hybrids segregating either human or rat chromosomes, the gene for histamine H1 receptor was found to reside on human chromosome 3 and rat chromosome 4.

The paramedian scalp reduction with posterior Z-plasty. A technique to minimize the "slot" defect

BACKGROUND

One consistent and undesired sequela resulting from scalp reductions has been the "slot" or "trough" defect, referring to the scar following the final reduction. Attempts to correct this have not been entirely satisfactory.

OBJECTIVE

To present an approach to minimize the "slot" defect that consists of staged modified paramedian scalp reductions combined with a large posterior Z-plasty during the final reduction.

METHODS

A paramedian crescent-shaped ellipse was marked onto the patient's scalp parallel and adjacent to the existing fringe hair. Subsequent reductions were performed in a similar manner approximately 2 months apart. The final reduction consisted of mobilization and transposition of the large flaps used in the posterior Z-plasty.

RESULTS

Patients who underwent the staged modified paramedian reductions combined with a posterior Z-plasty had significant minimization and adequate camouflage of the undesirable "slot."

CONCLUSION

Combining a large posterior Z-plasty with a paramedian reduction minimizes the slot defect.

Bretylium tosylate binds preferentially to muscarinic receptors labelled with [3H]oxotremorine M (SH or 'high affinity' receptors) in rat heart and brain cortex

Bretylium tosylate is an antiarrhythmic agent. In guinea pig atria it showed the properties of a competitive muscarinic (cholinergic) antagonist and could distinguish between two muscarinic receptor classes or states in cardiac membranes. We decided to further investigate its binding properties at muscarinic cholinergic receptors of the rat heart and brain (cortex), keeping in mind the recently discovered heterogeneity of muscarinic receptor protein. Bretylium tosylate recognized two receptor classes or states in the heart with Ki values of 0.9 and 11 microM. All cardiac membrane receptors showed a homogeneous (11 microM) Ki value for the drug in the presence of GTP in the incubation medium, or after in vivo pretreatment with islet activating protein (IAP). Bretylium tosylate was able (but only at a high concentration, 1 mM) to slow the dissociation kinetics of the tracer, which suggests that it also bound to an allosteric site on the muscarinic receptor, or that it affected the receptor environment. In the brain cortex, as in the heart, bretylium tosylate displayed a high affinity for receptors labelled with the agonist [3H]oxotremorine M (Ki value: 0.8 microM for the SH-or cardiac-type high-affinity receptors), and a 8- to 10-fold lower affinity for cortex M and L receptors. These data suggest that the antagonist bretylium tosylate had binding properties in rat cardiac membranes analogous to those of the partial agonist pilocarpine and that it interacted with a single type of receptor.

Characterization of muscarinic receptors: type M2 (subtype B) on neuro-2A neuroblastoma cells

The binding of the nonselective muscarinic antagonist, [3H]N-methylscopolamine (NMS) to a mouse neuroblastoma cell line (Neuro-2A) and its coupling to the inhibition of adenylate cyclase were characterized. Specific [3H]NMS binding to membrane preparations was rapid, saturable, and of high affinity. Saturation experiments revealed a single class of binding sites for the radioligand. Competition experiments with the muscarinic drugs pirenzepine, AF DX 116, dicyclomine and atropine revealed that the muscarinic receptors present on these cells are predominantly of a single class, subtype B (M2). In addition, agonist binding demonstrated existence of a GTP-sensitive high affinity binding state of the receptors. Coupling of these muscarinic receptors to the adenylate cyclase system was investigated using the muscarinic agonist carbachol which was able to inhibit the prostaglandin (PGE1)-stimulated activation of adenylate cyclase. The agonist carbachol did not stimulate the formation of IP3 above basal levels, which indicated that the receptors are not coupled to phosphatidylinositol metabolism. In conclusion, we show that possessing predominantly one subtype of muscarinic receptor, the Neuro-2A cells provide a useful model for the investigation of the heterogeneity of muscarinic receptors and the relationship of subtype to the coupling of different effectors.