Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:4.6.1.1 (adenylate cyclase)
 19,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Since acetylcholine (ACh) was identified as a neurotransmitter at parasympathetic nerve terminals by pioneering pharmacologists such as O. Schmiedeberg, R. Hunt, O. Loewi and H.H. Dale, muscarinic acetylcholine receptors (mACh-R) serving as a transducer of muscarinic action have been assumed to exist. After many tries to identify the mACh-R, it's existence was established by the group of S.H. Snyder, who employed binding assays with the radioligand 3H-QNB. The presence of a neuronal (M1) and a peripheral (M2) mACh-R was suggested from the action of an M1-specific agonist, McN-A-343; and this observation was followed by the discovery that the antagonist pirenzepine had higher affinity for M1 than for M2. Later, peripheral mACh-Rs were further subclassified in two types by the heart-specific action of gallamine and the different affinities of AF-DX116 and 4-DAMP. At present, three subtypes, M1 (neuronal), M2 (heart) and M3 (other peripheral organs), can be pharmacologically distinguished by affinity differences. On the other hand, purification of mACh-R and analysis by gene technology revealed the presence of five mACh-R mRNAs (m1-m5), which were expressed in various organs with different abundances. These subtypes couple with subcellular muscarinic responses through different GTP-binding proteins. The connection between the subtypes, GTP-binding proteins and responses is not fully understood yet. Our studies showed that in guinea pig heart, in which only m2 mRNA is expressed, muscarinic agonists recognize two subgroups (M2 alpha and M2 beta) with different affinities. One couples with the inhibition of adenylate cyclase, and the other couples with PI turnover through different GTP-binding proteins.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:[Progress in the study of muscarinic acetylcholine receptors; establishment of the subtypes or subgroups]. 210 3

Pharmacological differences between muscarinic cholinergic receptors coupled to phosphoinositide turnover and those coupled to adenylate cyclase were studied. Stimulation of muscarinic receptors from SK-N-SH human neuroblastoma cells resulted in phosphoinositide hydrolysis, but not in inhibition of cAMP formation. As has been shown previously, stimulation of muscarinic receptors from NG108-15 neuroblastoma x glioma cells, on the other hand, resulted in inhibition of cAMP formation without any observable phosphoinositide hydrolysis. These two cell lines provide a useful model system in which to study differential coupling of muscarinic cholinergic receptors. Inhibition of [3H]N-methyl scopolamine [( 3H]NMS) binding and inhibition of carbachol-stimulated function by the antagonists pirenzepine, AF-DX 116, and 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) were studied in this system. Pirenzepine inhibited [3H]NMS binding in both cell lines with low affinity (Ki of 130 and 160 nM in NG108-15 and SK-N-SH cells respectively), indicating that both cell lines express M2 receptors. None of the three antagonists studied exhibited any clear selectivity for the receptors in one cell line over those of the other. In contrast, several agonists including acetylcholine, bethanechol and carbachol exhibited pronounced selectivity. These agonists inhibited [3H]NMS binding to membranes from SK-N-SH cells with IC50 values that were 17-, 3- and 38-fold higher, respectively, than those of NG108-15 cells. This selectivity was still observed when whole cells rather than membranes were studied. These findings indicate that pharmacological differences between receptors coupled to phosphoinositide turnover and those coupled to cAMP inhibition can be detected with certain agonists, but not with the antagonists pirenzepine, AF-DX 116 or 4-DAMP.
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PMID:Pharmacological differences between muscarinic receptors coupled to phosphoinositide turnover and those coupled to adenylate cyclase inhibition. 247 34

The experiments were done to investigate the presence and subtype of functionally presynaptic muscarinic receptors in cholinergic nerves of the guinea pig urinary bladder. Bladder strips were incubated with 3H-choline and superfused with Tyrode's solution containing eserine. Secreted 3H-acetylcholine was separated from 3H-choline. The electrically evoked 3H-acetylcholine secretion increased with the stimulation frequency. 3H-Acetylcholine secretion was enhanced by muscarinic antagonists, was depressed by carbachol and by alpha adrenoceptor agonists but was not influenced by drugs acting at beta adrenoceptors or purinoceptors. The rank order for the enhancing effect of muscarinic antagonist EC50 values was propantheline < atropine < methylatropine < N-desethyloxybutynin < UH-AH 37 < benzhexol < AQ-RA 741 < 4-DAMP < procyclidine < emepronium < secoverine < oxybutynin < tropicamide < promethazine < himbacine < hexahydrosiladifenidol < methoctramine = pirenzepine < dicyclomine < AF-DX 116, and the EC50 values correlated best with constants for the M4/m4 muscarinic receptor subtype. The enhancing effect of atropine was counteracted by carbachol; the effects of atropine and emepronium were not additive. The 3H-acetylcholine secretion was also enhanced by forskolin, 3-isobutyl-1-methylxanthine, 8-bromo cyclic AMP and dibutyryl cyclic AMP. The combined effects of atropine and forskolin were additive. These results suggest that the 3H-acetylcholine secretion in the guinea pig urinary bladder is regulated by a presynaptic muscarinic autoreceptor of the M4 subtype that is not coupled to adenylate cyclase.
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PMID:Classification of the presynaptic muscarinic receptor subtype that regulates 3H-acetylcholine secretion in the guinea pig urinary bladder in vitro. 761 31

Pharmacological studies on pirenzepine (PZ), 4-diphenylacetoxy-N-methyl-piperidine (4-DAMP) and AFDX-116 antagonism of carbachol (CCh)-induced contraction, inositol trisphosphate (IP3) production and cAMP formation revealed the involvement of M3 receptors in these responses. The PA2 values for PZ and 4-DAMP antagonism to CCh-induced contraction were 7.1 and 9.0, respectively, and AFDX-116 had no effect on these responses. Further, 4-DAMP was a much more potent inhibitor than PZ of CCh-stimulation of IP3 production and cAMP formation. Both L-type calcium channel blockers, which inhibit Ca2+ influx, and BAPTA, an intracellular calcium chelator, inhibited these biochemical and pharmacological responses due to CCh. It is concluded that both intracellular and extracellular Ca2+ mobilization are involved in muscarinic stimulation of cAMP production, and that M3 receptors are coupled to the activation of both phospholipase C and adenylate cyclase in this tissue. The data presented here are consistent with previous work that stimulation of muscarinic receptors in dog iris sphincter with CCh (> 5 microM) increases intracellular cAMP levels.
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PMID:M3 muscarinic receptors mediate an increase in both inositol trisphosphate production and cyclic AMP formation in dog iris sphincter smooth muscle. 820 21

A functional role for the M2 muscarinic receptor in smooth muscle contraction was investigated in isolated guinea pig ileum. Contractile responses to the muscarinic agonist oxotremorine-M (oxo-M) were measured in isolated ilea that had been pretreated with histamine (0.32 microM) and isoproterenol (0.64 microM) to achieve conditions of elevated cAMP. The resulting concentration-effect curve was biphasic, consisting of high (0-50 nM) and low (> 50 nM) potency components. The reversible M2-selective antagonist AF-DX 116 ([[2-[(diethylamino)methyl]-1-piperidinyl]acetyl]-5,11- dihydro-6H-pyrido[2,3b][1,4]benzodiazepine-6-one) (1 and 10 microM) shifted this curve in a manner that was inconsistent with competitive antagonism at a single receptor site; the high affinity component was significantly blocked, whereas there was little effect on the low affinity portion of the curve. To inactivate the M3 muscarinic receptors selectively, ilea were incubated with the irreversible M1/M3-selective muscarinic antagonist 4-DAMP mustard [N-(2-chloroethyl)-4-piperidinyldiphenylacetate] (40 nM) for 1 hr in the presence of AF-DX 116 (1 microM) and were then washed extensively. Under these conditions, the contractile responses to oxo-M, in the presence of histamine and isoproterenol or forskolin, were antagonized by AF-DX 116 (1 microM) in a manner consistent with that mediated by an M2 receptor. AF-DX 116 caused 6.6- and 11-fold increases in the EC50 value for oxo-M for ilea pretreated with isoproterenol and forskolin, respectively, and a significant increase in the Hill coefficient in both cases. Under basal conditions, AF-DX 116 caused only a 1.34-fold increase in the EC50 value and no change in the Hill coefficient. In addition, under basal conditions 4-DAMP mustard treatment shifted the oxo-M contractile response curve to the right approximately 20-fold. However, when histamine was present in combination with isoproterenol or forskolin 4-DAMP mustard treatment shifted the concentration-effect curves for oxo-M to the right only about 3.5-fold. Oxo-M produced an M3-mediated stimulation of phosphoinositide hydrolysis in the longitudinal muscle of rat ileum with an EC50 value of 30 microM. 4-DAMP mustard (10 nM; 1 hr) prevented this response, resulting in a 6.6-fold increase in the EC50 value with a 65% reduction of the maximal response. In contrast, this treatment blocked M2-mediated inhibition of isoproterenol-stimulated adenylate cyclase with only a 2-fold increase in EC50, without affecting maximum inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Functional role for the M2 muscarinic receptor in smooth muscle of guinea pig ileum. 839 16

1. The affinities of 10 selective muscarinic receptor antagonists against [3H]-quinuclidinyl benzilate (QNB) binding were determined to characterize the muscarinic receptors present in guinea-pig gallbladder smooth muscle. The highest correlation was obtained for the comparison between the pKi values for the gallbladder smooth muscle and M2 sites. Pirenzepine revealed two binding sites with affinities indicating the presence of muscarinic M2 receptors in abundance and a minor population of an additional site(s). 2. Carbachol produced gallbladder contractions, stimulated phosphoinositide (PI) hydrolysis and inhibited cAMP formation concentration-dependently with pD2 values of 6.12 +/- 0.11, 5.18 +/- 0.33 and 7.19 +/- 0.15, respectively. 3. Pirenzepine, 4-DAMP, HHSiD, pF-HHSiD, AF-DX 116, methoctramine, AQ-RA 741, guanylpirenzepine and AF-DX 384 showed competitive antagonism against carbachol-induced gallbladder contractions. There was no correlation between the pA2 values for the gallbladder and pKi values for the M2 sites, whereas significant correlations were found for the M1, M3 and M4 sites, the best correlation being between the pA2 values for the gallbladder and M4 subtypes. 4. Finally, the presence of both m2 and m4 receptor proteins were demonstrated by Western blot analysis. It is concluded that guinea-pig gallbladder smooth muscle has both muscarinic M2 and M4 receptors, which are coupled to adenylate cyclase inhibition and PI hydrolysis. 5. Although it seems likely that M2 receptors do not play a primary role in carbachol-induced guinea-pig gallbladder contraction, the characterization of the muscarinic subtypes which mediate these contractile responses needs further evidence.
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PMID:Evidence for the presence of muscarinic M2 and M4 receptors in guinea-pig gallbladder smooth muscle. 978 89

The aim of this study was to identify the subtypes of muscarinic receptors that mediate in vivo and in vitro canine ileal longitudinal muscle contractions and whether their role is modulated by inflammation. Previous studies have reported that circular muscle contractions are suppressed in ileal inflammation induced by mucosal exposure to ethanol and acetic acid. We found that inflammation had no significant effect on in vivo and in vitro spontaneous or muscarinic receptor-mediated contractions of the longitudinal muscle. The longitudinal muscle contractions were mediated primarily by the M(3) receptor subtype. However, the IC(50) of the M(2) receptor antagonist methoctramine was only 10 times greater than that of the M(3) receptor antagonist 4-DAMP in the longitudinal muscle, whereas it was 224 times greater in the circular muscle. M(2) receptor-coupled decrease of intracellular cAMP occurred in the longitudinal but not in the circular muscle from the normal ileum. Inflammation did not alter this coupling in the longitudinal muscle but established it in the circular muscle. In conclusion, M(2) receptors may play a greater role in the mediation of longitudinal muscle contractions than circular muscle contractions. Inflammation does not alter the contractility or the relative role of muscarinic receptor subtypes in longitudinal muscle cells. However, it modulates the M(2) receptor coupling to adenylate cyclase in the circular muscle.
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PMID:Differential inflammatory modulation of canine ileal longitudinal and circular muscle cells. 1044 48

The presence of muscarinic (M) acetylcholine receptors in the noninnervated chick amnion makes it possible to analyze their functioning with presynaptic effects excluded. The M receptors of the amnion mediating its contraction were identified by testing with selective antagonists: pirenzepine for M1, methoctramine for M2, 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) for M3, and tropicamide for M4 receptor subtype. All antagonists acted as competitive inhibitors of M-acetylcholine receptors. With respect to cholinolytic activity estimated from the response to carbacholine (CBC) (-logIC50), the antagonists could be arranged in the following series: 4-DAMP (8.29) > tropicamide (6.97) > pirenzepine (5.85) > methoctramine (5.63). In addition, the effect of forskolin (5 microM), activator of adenylate cyclase (AC), was unidirectional with beta-adrenergic agonists; it blocked CBC-induced contractile activity of the amnion, whereas phospholipase C (1.25 U/ml) stimulated this activity. These data suggest that CBC- or acetylcholine (ACh)-induced contractile activity of the amnion is mediated by M3 acetylcholine receptors. Evaluation of contractile response to ACh by the tonic component usually revealed one pool of M3 acetylcholine receptors. One pool was also revealed after treatment with 4-DAMP, with the Hill coefficient being increased (ACh, n = 1.07; ACh against the 4-DAMP background, n = 1.48). It is possible to detect two pools of M3-acetylcholine receptors on the basis of either phase-frequency or tonic response, i.e., independently of the test parameter.
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PMID:[Muscarinic acetylcholine receptors of the chick amnion]. 1894 94