Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: DrugBank:EXPT02427 (Atropine)
 3,300 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

myo-[3H]Inositol-labelled SH-SY5Y cells were permeabilized with electrical discharges. 3H-Inositol phosphate formation in cells shown to be fully permeable was stimulated by the muscarinic agonist carbachol, by guanosine 5'-(gamma-thio)triphosphate [GTP(S)], and by guanosine 5'-(beta gamma-imido)diphosphate (GppNHp). Synergism was observed on coincubation of these GTP analogues with carbachol. GTP was also stimulatory and guanosine 5'-(beta-thio)diphosphate was inhibitory in the presence of agonist. Atropine blocked the effects of carbachol. Stimulation by GTP(S) (0.1 mM) occurred after a 1-2-min lag, whereas Ca2+ (0.5 mM), carbachol (1 mM), and carbachol plus GTP(S) stimulated without delay. The effects of carbachol plus GTP(S) but not those of Ca2+ were inhibited by spermine (4 mM). Accumulation of 3H-inositol phosphates was enhanced by Li+ (4 mM) only in intact cells. In intact or permeabilized cells, the "partial" agonist arecoline was maximally 40-50% as efficacious as carbachol. In permeabilized cells, the maximal effects of carbachol and arecoline were enhanced 2.8- and 5.3-fold, respectively, by 0.1 mM GTP(S), but only the EC50 for carbachol was substantially reduced. The binding affinity of carbachol but not that of arecoline in permeabilized cells was significantly reduced by 0.1 mM GppNHp. These data indicate that a guanine nucleotide-binding regulatory protein is involved in coupling muscarinic receptors to phosphoinositidase C in SH-SY5Y cells and that the activity of this protein influences the relationship between receptor occupation and phosphoinositide response.
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PMID:Regulation of muscarinic agonist-induced activation of phosphoinositidase C in electrically permeabilized SH-SY5Y human neuroblastoma cells by guanine nucleotides. 215 57

Particulate fractions from fresh bovine corneal endothelium exhibited high affinity, specific binding by a potent muscarinic cholinergic radioligand, [3H]QNB. Particulate fraction binding sites exhibited half maximal binding at approximately 0.3 nM [3H]QNB and reached a maximal binding capacity of 820 fmoles/mg of protein at 3 nM [3H]QNB. Muscarinic cholinergic antagonists and agonists competed with [3H]QNB when incubated concurrently with the tissue, showing relative potencies expected of these agents when binding to muscarinic cholinergic receptors. Particulate fractions prepared from cultured bovine corneal endothelium exhibited qualitatively similar [3H]QNB binding characteristics, but maximal binding capacity was only about one-fifth of its fresh-tissue counterpart. Intact cultured cells showed 3-fold more specific [3H]QNB binding than did their particulate fractions. Incubation of intact corneal endothelial cells with muscarinic cholinergic agonists such as carbachol stimulated cyclic [3H]GMP 3-fold from endogenous [3H]GTP within 1 min of incubation. The effect diminished rapidly and returned to control levels within 8 min. Carbachol stimulation of cyclic [3H]GMP was concentration-dependent, reaching half maximal stimulation at 1 microM. Atropine was a potent, competitive inhibitor of carbachol stimulation of cyclic [3H]GMP in endothelial cultures, requiring only 1 microM to completely block the carbachol response. These experiments demonstrate the existence of muscarinic cholinergic receptors in bovine corneal endothelium and their control of cyclic GMP levels in this tissue.
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PMID:Muscarinic receptors and their regulation of cyclic GMP in corneal endothelial cells. 215 50

1. The effects of activation of muscarinic receptors on the voltage-dependent calcium current, ICa, in parasympathetic neurones were examined. 2. Neurones were enzymatically isolated from the interatrial septum of bull-frog (Rana catesbeiana) heart, and were maintained in short-term (1-6 day) tissue culture. ICa was recorded from the cells using whole-cell patch-clamp methods (Clark, Tse & Giles, 1990). 3. External application of 2 nM to 10 microM acetylcholine (ACh) reduced the amplitude and slowed the time course of activation of ICa. These effects were dependent on membrane potential; they were most pronounced at potentials near the peak of the current-voltage relation for ICa (i.e. +10 to +15 mV), whereas at more-negative potentials (i.e. -15 to -25 mV) the effects on both amplitude and time course were relatively small. 4. Atropine (1 microM) completely blocked the action of 1 microM-ACh, indicating that the effects of ACh on ICa were mediated by activation of muscarinic receptors. 5. Other muscarinic agonists, such as carbamylcholine (0.1-10 microM), DL-muscarine (0.1-2.5 microM) and oxotremorine (5 microM), had similar effects on ICa to ACh. 6. A guanine nucleotide-binding protein (G-protein) is involved in this muscarinic inhibition of ICa. Inclusion of the non-hydrolysable guanosine triphosphate analogue guanosine 5'-O-(3-thiotriphosphate) (GTP-gamma-S; 200 microM) in the intracellular solutions mimicked the effects of ACh, and application of external ACh in the presence of internal GTP-gamma-S produced smaller changes in ICa than in control conditions. Inclusion of another non-hydrolysable analogue, guanosine 5'-O-(2-thiodiphosphate) (GDP-beta-S; 0.5-5 mM), blocked the inhibitory effect of ACh on ICa. 7. The G-protein involved in the inhibition of ICa was sensitive to pertussis toxin (islet-activating protein; IAP). The inhibition of ICa by carbamylcholine (5 microM) was reduced by about 90% after incubating cells for 12-15 h in culture medium containing 200 ng/ml IAP. 8. The possible roles of cyclic AMP or cyclic GMP-dependent protein kinases, or protein kinase C, in the muscarinic inhibition of ICa were tested, but these enzymes appear not to be directly involved.
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PMID:Muscarinic modulation of calcium current in neurones from the interatrial septum of bull-frog heart. 217 Jun 34

Experiments were undertaken to determine whether the anticholinergic actions of tricyclic antidepressants are mediated by a selective interaction with a subclass of muscarinic receptors. To this end, the potencies of these antidepressants to inhibit [3H]-QNB binding to rat brain cerebral cortical membranes was compared to their potencies as antagonists of carbachol-stimulated inositol phosphate accumulation in cerebral cortical slices and carbachol-induced inhibition of GTP-stimulated adenylate cyclase in striatal membranes. Whereas amitriptyline was more potent than pirenzepine, a selective muscarinic M1 receptor antagonist, in competing for [3H]-QNB binding sites and as an antagonist of carbachol-induced inhibition of adenylate cyclase, pirenzepine was substantially more active (ten-fold) than amitriptyline in blocking carbachol-stimulated phosphatidyl inositol turnover. Atropine was more potent than all other agents in these assays, failing to display any significant degree of selectivity. The results suggest that the tricyclic antidepressants, in particular amitriptyline, appear to be selective antagonists for muscarinic receptors associated with adenylate cyclase in striatal membranes. Given the current classification of cholinergic receptors, these findings indicate that the tricyclic antidepressants may be useful for defining the properties of M2 receptors in brain.
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PMID:Selective interaction of tricyclic antidepressants with a subclass of rat brain cholinergic muscarinic receptors. 303 13

The muscarinic antagonist 1-[benzilic 4,4'-3H]-quinuclidinyl benzilate [3H]-QNB) bound to a single class of non-cooperative sites in calf cerebral cortex membranes (KD = 0.29 nM and Bmax = 1.06 pM/mg protein). Computer-assisted analysis of the shallow pirenzepine/[3H]-QNB competition binding curves indicated that 68% of these sites were of the M1-subtype and the remaining 32% of the M2 subtype. Respective Ki-values for pirenzepine were 27 nM and 1.14 microM. Binding characteristics of the antagonist atropine and of the agonist carbachol for M2 were evaluated by performing competition binding with 0.5 nM [3H]-QNB in the presence of 2 microM pirenzepine. The binding characteristics for the M1 receptors were obtained indirectly by subtracting the curve for M2 from the total curve, or directly by competition binding with 0.3 nM [3H]-pirenzepine. Atropine competition curves were steep for M1 and M2 and were not affected by 1 mM GTP nor by 1 mM N-ethylmaleimide. The carbachol competition curve was shallow for M2. The steep curves for M1 indicate that this receptor subclass was only composed of low agonist affinity sites. GTP, which caused a rightward shift and a steepening of the carbachol competition curve for M2, did not affect the curves for M1. N-ethylmaleimide provoked a leftward shift and a steepening of the carbachol competition curve for M2 and abolished GTP modulation. A leftward shift was also observed for M1, but of a smaller magnitude (i.e. 3-4-fold for M1 compared to 17-fold for M2). These data suggest that, in calf brain cortex, M1 and M2 receptors show different susceptibility towards GTP and N-ethylmaleimide modulation.
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PMID:Different agonist binding properties of M1 and M2 muscarinic receptors in calf brain cortex membranes. 368 39

Acetylcholine (ACH) produced specific inhibition of Na, K-ATP-ase activity in sarcolemmic preparations of the frog heart (K0.5 = 1 microM), dog atria (K0,5 = 5 microM) and ventricles (K0.5 = 1 microM), and dog small intestinal smooth muscles (K0,5 = 0.5 microM). K0.5 is the concentration causing a half-maximal effect. Atropine (10(-7) = 10(-6) M) blocked the inhibitory effect of ACH. The preparations contained a considerable number of 3H-quinuclidinyl benzilate (3H-QNB) binding sites. Treatment of atrial sarcolemma with a mixture of digitonin and sodium cholate resulted in a substantial decrease in the number of 3H-QNB binding sites in the membrane, while Na,K-ATPase lost responsiveness to ACH. In the presence of 10 microM GTP there was a noticeable decrease in sensitivity of the enzyme to ACH. It is assumed that inhibition of Na, K-ATPase activity by acetylcholine is mediated by muscarinic receptor activation with the involvement in this process of GTP-binding proteins.
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PMID:[M-cholinoreceptor-mediated inhibition of Na, K-ATPase activity in the myocardial sarcolemma and intestinal smooth muscles by acetylcholine]. 609 7

The inhibitory pathway of cardiac cAMP-dependent protein kinase regulated Cl- conductance was investigated using the whole-cell configuration of patch-clamp techniques in single guinea pig ventricular myocytes. Pertussis toxin-sensitive G proteins (Gi), mediating the signal transductions between muscarinic receptors and adenylate cyclase, have a substantial tonic activity even in the absence of muscarinic receptor modulators. Muscarinic agonists or antagonists (like atropine) either increase or decrease this basal activity of Gi by altering the proportion of active and inactive forms of the receptors. Similar to L-type Ca-channel currents, the Cl- conductance showed a transient over-recovery upon cessation of brief muscarinic receptor stimulation by carbachol (CCh) (rebound). Atropine alone enhanced the Cl- conductance elicited by low concentrations of Iso (reverse agonist). After washout of atropine, the over-suppression of the conductance was observed as a mirror image of CCh-induced rebound (reverse rebound). Both types of rebound became prominent when cell dialysis with pipette solutions containing 100 microM GTP was minimized with high-resistance pipettes. Endogenous GTP is therefore an intracellular modulator, and not simply a mediator, of Gi-dependent signal transduction.
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PMID:Inhibitory pathway of cardiac PKA-dependent Cl- conductance via pertussis toxin-sensitive G proteins. 775 28

Many important airway epithelial cell functions are regulated by intracellular cAMP. Adenylyl cyclase, the enzyme that synthesizes cAMP, is under dual regulation in many cells, but muscarinic agonists have not been shown to inhibit adenylyl cyclase in human and dog epithelial cells, despite the presence of muscarinic receptors. We question whether the lack of inhibition was related to the absence of a component of the inhibitory pathway or a lack of coupling between the components. The GTP-binding regulatory proteins (G proteins) that regulate adenylyl cyclase activity in airway epithelium have not been well characterized. We used primary cultures of guinea pig tracheal epithelial cells as a model system and identified the G proteins that modulate adenylyl cyclase activity. Immunoblot analysis demonstrated the presence of alpha subunits corresponding to stimulatory (Gs alpha) and inhibitory [Gi alpha (2) and Gi alpha (3)] G proteins as well as beta chains. These G proteins were functionally coupled to stimulation and inhibition of adenylyl cyclase in epithelial membrane preparations. Pertussis toxin-catalyzed [32P]ADP-ribosylation of Gi alpha was significantly reduced by 100 microM GTP gamma S (78.4 +/- 3.6% of control), by 100 mM NaF (41.9 +/- 9.1% of control), and by carbachol (100 microM) (29.2 +/- 9.0% of control). Atropine (10 microM) inhibited the carbachol effect by greater than 90%, suggesting that the muscarinic receptors were functionally coupled to Gi proteins. beta-Adrenergic agonists increased adenylyl cyclase activity, but muscarinic agonists failed to inhibit this enzyme. In summary, guinea pig tracheal epithelial membranes contain muscarinic receptors, Gi alpha (2) and adenylyl cyclase, which are appropriately coupled.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Characterization of GTP-binding proteins coupled to inhibition of adenylyl cyclase in guinea pig tracheal epithelial cells. 800 43

1. The whole-cell patch clamp and intracellular perfusion techniques were used for studying the effects of atropine and other muscarinic acetylcholine receptor (mAChR) antagonists on the L-type calcium currents (ICa) in frog and rat ventricular myocytes, and on the mAChR-activated K+ current (IK(ACh)) in frog atrial myocytes. 2. In frog ventricular myocytes, atropine (0.1 nM to 1 microM) reversed the inhibitory effect of acetylcholine (ACh, 1 nM) on ICa previously stimulated by isoprenaline (Iso, 2 microM), a beta-adrenergic agonist. However, in the concomitant presence of Iso, ACh and atropine, ICa was > 50% larger than in Iso alone. 3. The effects of atropine were then examined in the absence of mAChR agonists. After a preliminary stimulation of ICa with Iso (0.1 or 2 microM), atropine induced a dose-dependent stimulation of ICa. EC50 (i.e. the concentration of atropine at which the response was 50% of the maximum) and Emax (i.e. maximal stimulation of ICa expressed as percentage increase in ICa with respect to the level in Iso alone) were respectively 0.6 nM and 35%. The stimulatory effect of atropine on ICa was not voltage dependent. 4. Atropine (1 microM) had no effect on frog ICa (i) under basal conditions, (ii) upon stimulation of ICa by the dihydropyridine agonist (-)-Bay K 8644 (1 microM), or (iii) when ICa had been previously stimulated by intracellular perfusion with cyclic AMP (3 microM). However, atropine increased ICa after a stimulation by forskolin (0.3 microM). Therefore, an increased adenylyl cyclase activity was required for atropine to produce its stimulatory effect on ICa. 5. The order of potency of mAChR antagonists to reverse the inhibitory effect of ACh on Iso elevated ICa in frog ventricle was atropine > AF-DX 116 >> pirenzepine. In the absence of ACh, mAChR antagonists produced their stimulatory effect on Iso elevated ICa with the same order of potency. 6. Intracellular substitution of Gpp(NH)p (5'-guanylylimidiphosphate) for GTP (420 microM) induced a strong inhibition of frog ICa in the presence of Iso (2 microM). This effect was attributed earlier to the spontaneous and irreversible activation of the GTP-binding regulatory protein (G protein), Gi, responsible for adenylyl cyclase inhibition. Atropine (1 microM) slowed down by a factor of 2 the rate of ICa inhibition induced by Gpp(NH)p. 7. In frog atrial myocytes, intracellular perfusion with 1 mM Gpp(NH)p induces spontaneous activation of IK(ACh). This effect was attributed earlier to the spontaneous and irreversible activation of the G protein, GK.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Agonist-independent effects of muscarinic antagonists on Ca2+ and K+ currents in frog and rat cardiac cells. 835 Feb 80

Characterization of adrenergic receptors in membranes from the rat seminal vesicle was studied by radioligand binding assay. Seminal vesicle membranes contained saturable and high affinity binding sites for the beta-adrenergic receptor antagonist 3H-dihydroalprenolol (3H-DHA) and for the alpha-adrenergic antagonist 3H-prazosin. The observed order of potency for adrenergic agonists in competing for the 3H-DHA binding sites: isoproterenol > epinephrine congruent to salbutamol > norepinephrine indicates that these membrane receptors have the properties of beta 2-adrenergic receptors. alpha 1-Adrenergic receptors were defined mainly as alpha 1A subtypes by demonstrating their insensitivity to pretreatment with chlorethylclonidine and the different rank orders of antagonist affinities. No significant binding sites for the alpha 2-adrenergic receptor agonist 3H-clonidine were observed. The GTP-induced reduction in the affinity of alpha 1-adrenergic receptors for epinephrine was significantly reversed by the muscarinic cholinergic agonist carbachol. Atropine effectively antagonized this effect of carbachol on the competitive inhibition of 3H-prazosin binding by epinephrine in the presence of GTP, which suggests that muscarinic cholinergic receptors regulate the affinity of alpha 1-adrenergic receptors by modulating the effect of guanine nucleotides. The effect of GTP on decreasing the affinity of beta 2-adrenergic receptors was not influenced by the addition of carbachol.
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PMID:Characterization of adrenergic receptors in membranes from the rat seminal vesicle. 838 73


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