A possible mechanism for diisopropylfluorophosphate-induced memory loss in rats

Passive avoidance retention and cortical [H3]-quinuclidinyl benzilate (QNB) binding were examined in rats that were chronically treated with diisopropylfluorophosphate (DFP), an irreversible acetylcholinersterase inhibitor. Retention of a passive avoidance response in DFP-treated rats was significantly lower when compared to vehicle-treated controls. Passive-avoidance retention decreased from 93% in control animals to 68% in DFP-treated rats. QNB binding studies revealed the density of muscarinic receptors in cortical homogenates was significantly reduced from 0.95 +/- 0.04 pmole/mg protein in controls to 0.72 +/- 0.04 pmole/m protein in DFP-treated rats. Scatchard analysis of QNB binding curves did not reveal a decrease in affinity of muscarinic receptors for QNB. Based on data that DFP causes a reduction in cholinergic receptors, this study supports the hypothesis that central cholinergic receptors are associated with mechanisms involved in memory storage.     

Biochemical and autoradiographic analysis of beta-adrenoceptors in rat nasal mucosa

The specific binding of 125I-(-)-cyanopindolol (125I-(-)-CYP) to homogenates and cryostat sections of rat nasal mucosa was saturable, stereoselective and of high affinity (Kd = 5.0 +/- 0.4 pM. Bmax = 204 +/- 12 fmol/mg protein and Kd = 7.2 +/- 0.7 pM; Bmax = 15 +/- 1 fmol/mg protein respectively). The subtype-selective antagonists, LK203-030 and ICI118,551, inhibited specific 125I-(-)-CYP binding according to a two-binding site model, indicating the presence of 57 and 45% beta 1-adrenoceptors in homogenates and cryostat sections, respectively. Competition of isoprenaline for antagonist binding to homogenates demonstrated 30 +/- 3% high-affinity agonist binding sites. A steepening of the curve was observed in presence of guanine nucleotides. In vitro labelling of cryostat sections of rat nasal mucosa was combined with autoradiography. The autoradiographs generated after incubation with 20 pM 125I-(-)-CYP showed specific labelling of the epithelium and glandular excretory ducts. It appeared from autoradiographs generated with subtype-selective antagonists in addition to the radioligand that beta 1- and beta 2-adrenoceptors were present in both structures.     

The effect of the plasticizers TBEP (tris-(2-butoxyethyl)-phosphate) and DEHP (di-(2-ethylhexyl)-phthalate) on beta-adrenergic ligand binding to alpha 1-acid glycoprotein and mononuclear leukocytes

The plasticizers tris-(2-butoxyethyl)-phosphate (TBEP) and di-(2-ethylhexyl)-phthalate (DEHP) and the beta-adrenergic receptor-blockers [3H]-(-)-dihydroalprenolol ([3H]-(-)-DHA) and [3H]-(-)-CGP 12177 were tested for their ability to interact with beta-adrenergic binding to alpha 1-acid glycoprotein (AAG) and mononuclear leukocytes (MNL). The IC50-values, obtained by displacement of [3H]-(-)-DHA bound to AAG, were 3.5 nM, 2 microM and 4 microM for TBEP, (-)-alprenolol and DEHP, respectively. (+/-)-CGP 12177 had virtually no effect on radioligand binding to AAG. The [3H]-(-)-CGP 12177 binding to MNL consisted of beta-adrenergic receptor binding (Kd = 210 pM) and non-saturable binding. [3H]-(-)-DHA was bound to two different classes of binding sites on MNL, the beta-adrenergic receptors (Kd = 440 pM) and a secondary class of binding sites (Kd = 64 nM). (+/-)-CGP 12177 displaced about 30% of [3H]-(-)-DHA from MNL with an IC50-value of 190 pm. (-)-ALP displaced about 85% of total bound radioligand and gave a biphasic displacement curve with IC50-values of 320 pM and 690 mM, respectively. TBEP displaced a considerable fraction of [3H]-(-)-CGP 12177 and [3H]-(-)-DHA bound to MNL beta-adrenergic receptors, whereas DEHP had no effect. In contrast, DEHP caused displacement of [3H]-(-)-DHA from the MNL low affinity sites, but was a markedly less potent displacer compared to TBEP. The present study shows that TBEP and DEHP interact with beta-adrenergic transport proteins, non-specific tissue binding sites and beta-adrenergic receptors coupled to adenylate cyclase. Plasticizers may thus affect the biology and pharmacology of the beta-adrenergic signal system.     

[3H]-Quinuclidinyl benzilate binding to muscarinic receptors in rat brain: comparison of results from intact brain slices and homogenates.

1. The binding of [3H]-( +/- )-quinuclidinyl benzilate ([3H]-( +/- )-QNB) to muscarinic sites in rat brain slice and homogenate preparations was compared. 2. Evidence is presented in support of the view that only the (-)-enantiomer of QNB binds with high affinity to muscarinic sites. 3. The Kd value for [3H]-(-)-QNB binding in slices was eight times higher than that measured in homogenates. 4. Similarly, the potencies of various muscarinic ligands as inhibitors of [3H]-(-)-QNB binding were consistently lower in slices than in homogenates. 5. It is proposed that the results may reflect differences in the binding properties of muscarinic receptors in intact tissue slice and homogenate preparations.     

Decreased binding of the muscarinic antagonist [3H]N-methylscopolamine in mouse brain following acute treatment with an organophosphate

The effect of the irreversible acetylcholinesterase inhibitor diisopropylfluorophosphate (DFP) on mouse brain muscarinic acetylcholine receptors was assessed using the muscarinic antagonists [3H]N-methylscopolamine [( 3H]NMS) and [3H]quinuclidinyl benzilate [( 3H]QNB). No alteration in the maximal binding capacity (Bmax) or equilibrium dissociation constant (KD) was observed in brain homogenates obtained from mice 12 h after a single injection of DFP when [3H]NMS was employed as the ligand. However, one administration of DFP produced a 24 and 33% decrease in Bmax as measured by [3H]NMS binding after 18 and 24 h, respectively. A similar decrease in Bmax was found after two (31%) and three (29%) days of daily DFP treatment. On the other hand, Scatchard analysis using [3H]QNB binding in the brain revealed no difference in KD or Bmax between untreated and 24 h DFP-treated mice. Thus, there is a differential alteration in mouse brain muscarinic acetylcholine receptors using these two ligands which suggests that [3H]NMS binding sites are more sensitive to regulation following acute organophosphate administration.     

Muscarinic receptor subtype specificity of 5'-(isobutylthio)-adenosine (SIBA) and its analogs

1. 5'(Isobutylthio)-adenosine (SIBA) and its analogs, at 100 microM, inhibited [3H]N-methyl-scopolamine binding to homogenates of whole brain and cortex (mainly M1 subtype receptors) by 11-30% and to cerebellum (mainly M2 subtype receptors) by 20-39%. 2. At 0.01-1.0 microM, stimulation of [3H]QNB and NMS-inaccessible [3H]QNB binding was observed, with the most induced by 1 microM 3-deaza-SIBA. 3. In contrast, [3H]pirenzepine ([3H]PZ) binding to whole brain and cortex was inhibited in a dose-dependent manner with Ki values in the microM range. 4. As antagonists of acetylcholine-induced contraction of guinea pig ileum (mainly M2 subtype receptors), the analogs were slightly more potent than pirenzepine, but several orders of magnitude less than atropine; the order of potency was opposite that determined for the binding of [3H]PZ to cortex. 5. Thus, SIBA and its analogs may have differential effects on muscarinic receptor subtypes and show some specificity for the M1 receptor subtype.     

Identification of drug receptors in porcine dental pulp by the radioligand binding assay

1. The acetylcholine (ACh), histamine and serotonin (5-HT) receptors in porcine dental pulp were characterized by the radioligand binding assay. 2. For [3H]nicotine binding site, Kd was 8.06 +/- 1.65 nM and Bmax was 270.83 +/- 32.68 fmol/mg protein. 3. For [3H]QNB binding site, Kd was 1.04 +/- 0.14 nM and Bmax was 24.83 +/- 3.09 fmol/mg protein. 4. For [3H]histamine binding site, Kd was 1.22 +/- 0.1 nM and Bmax was 283.15 +/- 33.1 fmol/mg protein. 5. For [3H]5-HT binding site, Kd was 1.41 +/- 0.1 nM and Bmax was 53.1 +/- 3.4 fmol/mg protein. 6. These findings indicate that the specific receptors for ACh, histamine and 5-HT are present in the porcine dental pulp, and that the ACh receptor is predominantly nicotinic.     

Effects of copper on the binding of agonists and antagonists to muscarinic receptors in rat brain

Studies were performed to assess the effects of copper treatment in vitro on muscarinic binding parameters in rat brain homogenates. Brainstem, an area low in copper, was found to be insensitive to copper treatment as compared to forebrain, a region of relatively high copper content. Inclusion of 3 microM copper in forebrain homogenates decreased the number of sites seen by [3H]-l-quinuclidinyl benzilate (QNB) by 40-50%. Copper-enhanced displacement of bound QNB was noted for agonists and antagonists. Both ligands showed maximal effects at 6 microM copper, although quantitative differences could be determined at any copper level. At levels of maximal effect, the increase in QNB displacement was greater than or less than 50% for agonists and antagonists respectively. Two-site analyses of carbamylcholine (CCH) binding showed that the addition of 1 microM copper to forebrain homogenates increased the percentage of high affinity sites (alpha) from 42 to 70%. The IC50 decreased from 3.1 to 1.7 microM, but the dissociation constants for the high and low affinity sites were not changed. The effect of added copper on CCH binding to muscarinic receptors was reversible with the addition of the copper-chelating agent triethylene tetramine.     

Pharmacological similarities between native brain and heterologously expressed alpha4beta2 nicotinic receptors

1 We studied the pharmacological properties of native rat brain and heterologously expressed rat alpha4beta2 nicotinic receptors immunoprecipitated onto a fixed substrate with the anti-alpha4 antibody mAb 299. 2 Immunodepletion with the anti-beta2 antibody mAb 270 showed that 89% of the mAb-299-precipitated rat brain receptors contained beta2. 3 The association and dissociation rate constants for 30 pM +/-[3H]-epibatidine binding to alpha4beta2 receptors expressed in oocytes were 0.02+/-0.01 and 0.03+/-0.01 min-1 (+/-standard error, degrees of freedom=7 - 8) at 20 - 23 degrees C. 4 The Hill coefficients for +/-[3H]epibatidine binding to the native brain, alpha4beta2 receptors expressed in oocytes, and alpha4beta2 receptors expressed in CV-1 cells (using recombinant adenovirus) were 0.69 - 0.70 suggesting a heterogeneous receptor population. Fits of the +/-[3H]-epibatidine concentration-binding data to a two-site model gave KD s of 8 - 30 and 560 - 1,200 pM. The high-affinity sites comprised 73 - 74% of the native brain and oocyte alpha4beta2 receptor population, 85% of the CV-1 alpha4beta2 receptor population. 5 The expression of rat alpha4beta2 receptors in CV-1 cells using vaccinia viral infection-transfection resulted in a more homogeneous receptor population (Hill coefficient of 1. 0+/-0.2). Fits of the +/-[3H]-epibatidine binding data to a single-site model gave a KD of 40+/-3 pM. 6 DHbetaE (IC50=260-470 nM) and the novel nicotine analogue NDNI (IC50=7-10 microM) inhibited 30 pM+/-[3H]-epibatidine binding to the native brain and heterologously expressed alpha4beta2 receptors equally well. 7 The results show that alpha4beta2-containing nicotinic receptors in the rat brain and heterologously expressed rat alpha4beta2 receptors have similar affinities for +/-[3H]-epibatidine, DHbetaE, and NDNI.     

Interaction of the neuromuscular blocking drugs alcuronium,decamethonium, gallamine,pancuronium, ritebronium,tercuronium and d-tubocurarine with muscarinic acetylcholine receptors in the heart and ileum

Neuromuscular blocking drugs have a high affinity for muscarinic acetylcholine receptors in the heart atria and ileal smooth muscle. In experiments on homogenates, alcuronium, gallamine, pancuronium, tercuronium and ritebronium inhibited the binding of the muscarinic antagonist (3H)quinuclidinyl benzilate (QNB) to rat heart atria with IC50 values of 0.15-0.53 mumol X 1(-1) and to ileal longitudinal muscles with IC50 values of 0.12-0.45 mumol X 1(-1). d-Tubocurarine and decamethonium inhibited (3H)QNB binding to these tissues with IC50 values of 6.2-8.5 mumol X 1(-1). For each neuromuscular blocking drug, the IC50 values were virtually identical for (3H)QNB displacement in the homogenates of the atria and of the ileal muscle. Alcuronium and gallamine differed from the other blocking agents in that they produced less steep (3H)QNB displacement curves both in the atria and the ileal muscle; Hill coefficients for the binding of alcuronium and gallamine to atrial and ileal homogenates were lower than unity. On isolated atria, gallamine, pancuronium, ritebronium and tercuronium antagonized the inhibition of tension development caused by the muscarinic agonist, methylfurmethide, with Kd values which were of the same order of magnitude as the IC50 values for the displacement of (3H)QNB binding to homogenates; the Kd of alcuronium was 12.5 times higher. d-Tubocurarine and decamethonium did not antagonize the effects of methylfurmethide at concentrations up to 100 mumol X 1(-1). On isolated ileal longitudinal muscle, gallamine and pancuronium antagonized the effects of methylfurmethide with Kd values that were 53 times and 100 times higher than their respective Kd values in the atria.(ABSTRACT TRUNCATED AT 250 WORDS)     

Positive cooperativity in the binding of alcuronium and N-methylscopolamine to muscarinic acetylcholine receptors

The effect of the neuromuscular blocker alcuronium on the binding of N-[3H]-methylscopolamine [( 3H]NMS) and l-[3H]quinuclidinylbenzilate ([3H]QNB) to muscarinic binding sites in rat heart atria, longitudinal smooth muscle of the ileum, cerebral cortex, cerebellum, and submaxillary glands was measured using filtration techniques. In the presence of 10(-5) M alcuronium, the binding of [3H]NMS (which was present at a subsaturating concentration of 2 x 10(-10) M) was increased 5.3-fold in the atria and smooth muscle and 3-fold in the cerebellum; no increase was observed in the brain cortex and salivary glands. The binding of [3H]NMS was inhibited at 10(-3) M and higher concentrations of alcuronium. The rates of [3H]NMS association to and dissociation from muscarinic binding sites in the atria were diminished by 10(-5) M alcuronium. Scatchard plots of [3H]NMS binding data obtained with and without 10(-5) M alcuronium indicated that the maximum number of binding sites was not altered by the drug, whereas the apparent Kd for [3H]NMS was diminished. In contrast to [3H] NMS, the effects of alcuronium on the binding of [3H]QNB were only inhibitory. The concentration of alcuronium required to diminish the binding of [3H]QNB by 50% (IC50) was 4-7 microM in the atria, ileal smooth muscle, and the cerebellum, 140 microM in the brain cortex, and 1200 microM in the parotid gland. The results suggest that the binding of low concentrations of alcuronium to muscarinic receptors in the heart, ileal smooth muscle, and cerebellum allosterically increases the affinity of muscarinic receptors towards [3H]NMS, although not [3H]QNB. At high concentrations, alcuronium inhibits the binding of muscarinic ligands, presumably by competition for the classical muscarinic binding site. Positive cooperativity induced by alcuronium appears to be specific for the m2 (cardiac) subtype of muscarinic receptors.     

Characterization of cholinergic muscarinic receptors in cow tracheal muscle membranes. Effect of maturation

The parasympathetic nervous system is important in the control of basal airway muscle tone and caliber. We characterized muscarinic cholinergic receptors in isolated tracheal membranes from cows of three age groups (immature, less than 2 weeks; transition, 3-5 months; and mature, greater than 5 years) using l-[3H]quinuclidinyl benzilate (l-[3H]QNB) as the radioligand. There were significant decreases in the densities of l-[3H]QNB binding sites with maturation (Bmax: 2344 +/- 169 vs 1381 +/- 85 vs 1116 +/- 80 fmol/mg protein for tissues from immature, transition and mature cows respectively). No change in the dissociation constant was observed with maturation (Kd: 0.38 +/- 0.09 vs 0.55 +/- 0.06 vs 0.50 +/- 0.07 nM for tissues from immature, transition and mature animals respectively). The association and dissociation rate constants did not vary between tissues from immature and mature animals. The specific activity of the enzyme, acetylcholinesterase, was correlated with the density of l-[3H]QNB binding sites present in the tracheal homogenates; that is, with maturation, there were significant decreases in acetylcholinesterase activity [0.28 +/- 0.01 vs 0.16 +/- 0.02 vs 0.08 +/- 0.01 mol X l-1 X min-1 X (mg protein)-1 for tissues from immature, transition and mature animals respectively]. All competition binding studies using muscarinic antagonists exhibited single site binding and did not show any differences in drug affinities between the age groups. In contrast, multiple binding sites were observed with carbachol, methacholine and muscarine, and there were significant decreases in receptor affinities for the muscarinic agonists. No changes in the proportion of high and low affinity sites were found. These results indicate that with maturation there are alterations in the properties of muscarinic receptors in tracheal smooth muscle.     

Adenosine receptors in basolateral membranes of rat renal cortex.

High affinity binding sites for adenosine were identified in rat kidney cortex basolateral membranes. Kinetic analysis indicates two sets of [3H]adenosine, [3H]ADO, binding sites, one with high affinity and Kd = 0.84 +/- 0.25 microM, one with low affinity and Kd = 4.74 +/- 0.37 microM. The ADO receptors were further characterized using ADO analogs as binding inhibitors. The most potent inhibitor of [3H]ADO binding was N-methyl-adenosine with a Kd of 5 microM, whereas 2-deoxyadenosine was about 50 times less potent. The binding of [3H]phenylisopropyladenosine, [3H]PIA, and [3H]-N-ethylcarboxamidoadenosine, [3H]NECA, to basolateral membranes was rapid and reversible. The Scatchard plot of [3H]PIA binding showed monophasic curves for experiments performed at 0 degrees C and 37 degrees C. The apparent Kd of [3H]PIA binding at 0 degrees C was 0.19 +/- 0.05 nM and 0.34 +/- 0.07 nM at 37 degrees C. The binding of [3H]NECA to basolateral membranes was found with an apparent affinity Kd of 110 +/- 50 nM at 0 degrees C. Pretreatment of membranes with N-ethylmaleimide (NEM) inhibited the [3H]PIA binding and did not affect the [3H]NECA binding. These results demonstrate that both A1 and A2 adenosine receptors are present in basolatertal membranes of rat kidney.     

Desensitization of histamine H1 receptor-mediated inositol phosphate accumulation in guinea pig cerebral cortex slices.

1. Histamine stimulated the production of [3H]-inositol phosphates in untreated (control) guinea-pig cerebral cortex slices with a best-fit EC50 of 17 +/- 4 microM, and a best-fit maximum response of 385 +/- 23% over basal accumulation. 2. Histamine pretreatment desensitized guinea-pig cortex slices to a subsequent challenge with histamine, which was observed as a reduction in the best-fit maximum response to 182 +/- 32% over basal accumulation. 3. The time-course for the histamine-induced production of [3H]-inositol phosphates was approximately linear over 90 min of stimulation in both control and histamine pretreated slices. The rate of production in pretreated slices was significantly slowed compared to control, such that by 90 min of histamine stimulation the desensitized slices produced 2.8 times the basal [3H]-inositol phosphate accumulation compared to 5.3 fold the basal [3H]-inositol phosphate accumulation in the control slices. 4. Displacement of [3H]-mepyramine binding to homogenates of guinea-pig cerebral cortex by mepyramine and histamine revealed that histamine pretreatment did not alter the apparent affinity of the H1 receptor for histamine (control Kd = 6.3 +/- 0.7 microM, desensitized Kd = 7.9 +/- 1.6 microM) or mepyramine (control Kd = 3.4 +/- 0.8 nM, desensitized Kd = 3.4 +/- 1.3 nM), nor was there any reduction in the calculated maximum number of [3H]-mepyramine binding sites (control Bmax = 192 +/- 31 fmol mg-1 protein, desensitized Bmax = 220 +/- 50 fmol mg-1 protein).(ABSTRACT TRUNCATED AT 250 WORDS)     

Binding of [3H](2S,1'S,2'S)-2-(9-xanthylmethyl)-2-(2'-carboxycyclopropyl)glycine ([3H]LY341495) to cell membranes expressing recombinant human group III metabotropic glutamate receptor subtypes

LY341495 is a highly potent and selective antagonist for group II mGlu receptors (mGlu2 and mGlu3). High affinity binding of [3H]LY341495 to recombinant human group II mGlu receptors (mGlu2 and mGlu3), and in rat brain homogenates (Kd approximately 1 nM), has been previously described. Although LY341495 is a very selective nM-potent antagonist for group II mGlu receptors, it is also a relatively potent antagonist for group III mGlu receptors at high nanomolar to low micromolar concentrations. In this study we examined and characterized the binding of [3H]LY341495 to membranes of cells expressing recombinant human group III mGlu receptors. Using up to 100 nM of [3H]LY341495, the level of specific binding in human mGlu4a receptor-expressing cell membranes was not appreciable and binding to this site was not examined further. In contrast, we demonstrated sufficient specific binding of [3H]LY341495 to human mGlu6, mGlu7a and mGlu8a receptor-expressing cell membranes to allow for further characterizations. [3H]LY341495 binding was saturable and rapidly reversible. [3H]LY341495 bound to a single site in each cell line, with Kd and Bmax values of 31.6+/-6.8 nM and 3.3+/-0.7 pmol/mg protein (mGlu6), 72.7+/-22.0 nM and 3.7+/-0.4 pmol/mg protein (mGlu7a), and 14.0+/-1.1 nM and 3.0+/-0.2 pmol/mg protein (mGlu8a). [3H]LY341495 binding to mGlu6, 7a and 8a was displaceable by compounds which interact functionally with group III mGlu receptors. For example, L-AP4 displaced [3H]LY341495 with Ki values of 6.8+/-3.1 microM (mGlu6), 211+/-43 microM (mGlu7a) and 1.6+/-0.3 microM (mGlu8a). With L-glutamate, we obtained Ki values of 12.3+/-3.5, 869+/-154 and 4.5+/-0.83 microM, for mGlu6, mGlu7a and mGlu8a, respectively. Ki values for unlabelled LY341495 were 0.058+/-0.008, 0.22+/-0.05 and 0.029+/-0.008 microM, respectively. These studies demonstrated that [3H]LY341495 is a useful radioligand for studying the pharmacology and expression of recombinant mGlu6, 7a and 8a receptors in cell lines.     

新抗胆碱药[3H]三环哌酯对人脑M受体的作用

用放射配体受体结合试验法,研究了新化合物三环哌酯与人大脑皮质M受体的结合特性,并与QNB作了比较。饱和实验结果显示,[³H]三环哌酯的结合参数与[³H]QNB相近,两种配体的作用均符合单位点模型。竞争性抑制实验结果表明二者作用强度相当。[³H]三环哌酯的结合和解离速率常数均较[³H]QNB大,且其与皮质M受体的解离受季铵酚的变构调节,结果提示,两种配体与M受体有一些不同的结合特性,在M受体研究中,[³H]三环哌酯可以作为[³H]QNB的补充工具。     

Selectivity of oxomemazine for the M1 muscarinic receptors

The binding characteristics of pirenzepine and oxomemazine to muscarinic receptor were studied to evaluate the selectivity of oxomemazine for the muscarinic receptor subtypes in rat cerebral microsomes. Equilibrium dissociation constant (KD) of (-)-[3H]quinuclidinyl benzilate([3H]QNB) determined from saturation isotherms was 64 pM. Analysis of the pirenzepine inhibition curve of [3H]QNB binding to cerebral microsome indicated the presence of two receptor subtypes with high (Ki = 16 nM, M1 receptor) and low (Ki = 400 nM, M3 receptor) affinity for pirenzepine. Oxomemazine also identified two receptor subtypes with about 20-fold difference in the affinity for high (Ki = 84 nM, OH receptor) and low (Ki = 1.65 microM, OL receptor) affinity sites. The percentage populations of M1 and M3 receptors to the total receptors were 61:39, and those of OH and OL receptors 39:61, respectively. Both pirenzepine and oxomemazine increased the KD value for [3H]QNB without affecting the binding site concentrations and Hill coefficient for the [3H]QNB binding. Oxomemazine had a 10-fold higher affinity at M1 receptors than at M3 receptors, and pirenzepine a 8-fold higher affinity at OH receptors than at OL receptors. Analysis of the shallow competition binding curves of oxomemazine for M1 receptors and pirenzepine for OL receptors yielded that 69% of M1 receptors were of OH receptors and the remaining 31% of OL receptors, and that 29% of OL receptors were of M1 receptors and 71% of M3 receptors. However, M3 for oxomemazine and OH for pirenzepine were composed of a uniform population. These results suggest that oxomemazine could be classified as a selective drug for M1 receptors and also demonstrate that rat cerebral microsomes contain three different subtypes of M1, M3 and the other site which is different from M1, M2 and M3 receptors.     

Single-site model of the neuronal 5-hydroxytryptamine uptake and imipramine-binding site

Recently, a high affinity [3H]imipramine-binding site of protein nature that appeared to be related to the 5-hydroxytryptamine (5-HT, serotonin) uptake mechanism was demonstrated. This binding site was only part of desipramine-displaceable [3H]imipramine binding, which contained a significant amount of additional binding not related to 5-HT uptake. The present study further investigates the [3H]imipramine-binding site of protein nature in the rat brain. Displacement by 5-HT and 6-methoxytetrahydro-beta-carboline (6-MeO-TH beta C) revealed monophasic displacement patterns with 60% displaceable binding. This binding fraction was abolished by protease treatment of the brain tissue prior to binding assay. Saturation studies of [3H]imipramine binding (1-30 nM) in rat cortex showed that the binding displaced by 30 microM 5-HT [Bmax 322 +/- 16 fmol/mg of protein, Kd 4.17 +/- 1.07 nM (means +/- SE)] was not different from the binding displaced by 1.0 microM norzimeldine (Bmax 349 +/- 15 fmol/mg of protein, Kd 4.47 +/- 1.07 nM) or 30 microM 6-MeO-TH beta C (Bmax 439 +/- 28 fmol/mg of protein, Kd 5.49 +/- 1.09 nM). When 100 microM desipramine was used in saturation studies, the binding was different from that displaced by 5-HT with Bmax 608 +/- 42 fmol/mg of protein and Kd 6.68 +/- 1.09 nM. Both displacement and saturation studies in which two displacing agents were combined indicated that most of the binding competed by 5-HT (30 microM) and norzimeldine (1.0 microM) is identical. Similarly, the binding displaced by 5-HT or norzimeldine is subsumed within 6-MeO-TH beta C (30 microM)-displaceable binding. Lesion studies with parachloroamphetamine, a selective toxin for 5-HT terminals, which resulted in a 83% reduction of [3H] 5-HT uptake ( [3H]noradrenaline uptake unaffected), abolished cortical [3H]imipramine binding displaced by 30 microM 5-HT or 1.0 microM norzimeldine. (greater than 80% reduction). However, with 100 microM desipramine as displacer, 40% of the binding remained in lesioned animals. The [3H]imipramine binding displaced by 30 microM 5-HT or 1.0 microM norzimeldine was sodium dependent, and an increase in NaCl concentration from 0 to 120 mM resulted in a 10-fold increase in affinity without effect on Bmax, whereas no change in binding was observed with increasing concentrations of LiCl.(ABSTRACT TRUNCATED AT 400 WORDS)     

Alpha 2-adrenoceptor subtypes and imidazoline-like binding sites in the rat brain.

1. The binding of [3H]-yohimbine and [3H]-idazoxan to rat cortex and hippocampus is rapid, reversible and of high affinity. Saturation data indicate that a single population of binding sites exist for [3H]-yohimbine in the cortex (Bmax 121 +/- 10 fmol mg-1, protein; Kd 5.2 +/- 0.9 nM) and hippocampus (Bmax 72 +/- 6 fmol mg-1 protein; Kd 5.8 +/- 0.7 nM). [3H]-idazoxan labels one site in the cortex (Bmax 87 +/- 8 fmol mg-1 protein; Kd 4.1 +/- 0.9 nM) and hippocampus (Bmax 30 +/- 6 fmol mg-1 protein; Kd 3.5 +/- 0.5 nM), when 3 microM phentolamine is used to define non-specific binding. A second distinct [3H]-idazoxan binding site (Bmax 110 +/- 21 fmol mg-1 protein; Kd 3.6 +/- 0.07 nM) is identified in rat cortex if 0.3 microM cirazoline is used to define non-specific binding and 3 microM yohimbine is included to prevent binding to alpha 2-adrenoceptors. 2. Displacement studies indicate that the alpha 1-adrenoceptor antagonist prazosin and the 5-HT1 ligands 8-OH-DPAT, RU 24969 and methysergide differentiate [3H]-yohimbine binding into two components; a high and low affinity site. In contrast the displacement of [3H]-idazoxan by each ligand was monophasic. 3. The affinities of 8-OH-DPAT, RU 24969 and methysergide determined against [3H]-idazoxan binding to the cortex and hippocampus correlate significantly with the binding site displaying low affinity for prazosin and previously designated alpha 2A. In contrast, a poor correlation exists for the high affinity site for prazosin designated alpha 2B.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characteristics of 5-HT3 binding sites in NG108-15, NCB-20 neuroblastoma cells and rat cerebral cortex using [3H]-quipazine and [3H]-GR65630 binding.

1. The biochemical and pharmacological properties of 5-HT3 receptors in homogenates of NG108-15 and NCB-20 neuroblastoma cells and rat cerebral cortex have been ascertained by the use of [3H]-quipazine and [3H]-GR65630 binding. 2. In NG108-15 and NCB-20 cell homogenates, [3H]-quipazine bound to a single class of high affinity (NG108-15: Kd = 6.2 +/- 1.1 nM, n = 4; NCB-20: Kd = 3.0 +/- 0.9 nM, n = 4; means +/- s.e.means) saturable (NG108-15: Bmax = 1340 +/- 220 fmol mg-1 protein; NCB-20: Bmax = 2300 +/- 200 fmol mg-1 protein) binding sites. In rat cortical homogenates, [3H]-quipazine bound to two populations of binding sites in the absence of the 5-hydroxytryptamine (5-HT) uptake inhibitor, paroxetine (Kd1 = 1.6 +/- 0.5 nM, Bmax1 = 75 +/- 14 fmol mg-1 protein; Kd2 = 500 +/- 300 nM, Bmax2 = 1840 +/- 1040 fmol mg-1 protein, n = 3), and to a single class of high affinity binding sites (Kd = 2.0 +/- 0.5 nM, n = 3; Bmax = 73 +/- 6 fmol mg-1 protein) in the presence of paroxetine. The high affinity (nanomolar) component probably represented 5-HT3 binding sites and the low affinity component represented 5-HT uptake sites. 3. [3H]-paroxetine bound with high affinity (Kd = 0.02 +/- 0.003 nM, n = 3) to a site in rat cortical homogenates in a saturable (Bmax = 323 +/- 45 fmol mg-1 protein, n = 3) and reversible manner.(ABSTRACT TRUNCATED AT 250 WORDS)