Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.1.7 (acetylcholinesterase)
 28,390 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The purification of axonal membranes of crustaceans was followed by measuring enrichment in [3H]tetrodotoxin binding capacity and in Na+, K+-ATPase activity. A characteristic of these membranes is their high content of lipids and their low content of protein as compared to other types of plasmatic membranes. The axonal membrane contains myosin-like, actin-like, tropomyosin-like, and tubulin-like proteins. It also contains Na+, K+-ATPase and acetylcholinesterase. The molecular weights of these two enzymes after solubilization are 280,000 and 270,000, respectively. The molecular weights of the catalytic subunits are 96,000 for ATPase and 71,000 for acetylcholinesterase. We confirmed the presence of a nicotine binding component in the axonal membrane of the lobster but we have been unable to find [3H]nicotine binding to crab axonal membranes. The binding to axonal membranes og of the sodium channel, has been studied in detail. The dissociation constant for the binding of [3H]tetrodotoxin to the axonal membrane receptor is 2.9 nM at pH 7.4. The concentration of the tetrodotoxin receptor in crustacean membranes is about 10 pmol/mg of membrane protein, 7 times less than the acetylcholinesterase, 30 times less than the Na+, K+-ATPase, and 30 times less than the nicotine binding component in the lobster membrane. A reasonable estimate indicates that approximately only one peptide chain in 1000 constitutes the tetrodotoxin binding part of the sodium channel in the axonal membrane. Veratridine, which acts selectively on the resting sodium permeability, binds to the phospholipid part of the axonal membrane. [3H]Veratridine binding to membranes parallels the electrophysiological effect. Veratridine and tetrodotoxin have different receptor sites. Although tetrodotoxin can repolarize the excitable membrane of a giant axon depolarized by veratridine, veratridine does not affect the binding of [3H]tetrodotoxin to purified axonal membranes. Similarly, tetrodotoxin does not affect the binding of [3H]veratridine to axonal membranes. Scorpion neurotoxin I, a presynaptic toxin which affects both the Na+ and the K+ channels, does not interfere with the binding of [3H]tetrodotoxin or [3H]veratridine to axonal membranes. Tetrodotoxin, veratridine, and scorpion neurotoxin I, which have in common the perturbation of the normal functioning of the sodium channel, act upon three different types of receptor sites.
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PMID:Constitution and properties of axonal membranes of crustacean nerves. 0 58

1 A number of criteria for considering adenosine 5'-triphosphate (ATP) as a neurotransmitter in the guinea-pig urinary bladder have been examined. In addition, the effect of tachyphylaxis to ATP on the response to non-adrenergic, non-cholinergic nerve stimulation has been re-examined.2 Quinacrine fluorescence histochemistry revealed a population of nerve fibres, ganglion cells, and nerve bundles in the bladder which were not seen in either the iris or vas deferens, where adrenergic and cholinergic nerves predominate. The distribution and morphology of the quinacrine-positive nerves in the bladder were different from those observed with catecholamine fluorescence and cholinesterase histochemistry, and were unaffected by chemical sympathectomy.3 Release of ATP from the bladder during stimulation of intramural excitatory nerves, in the presence of atropine and guanethidine increased to 3-12 times prestimulation levels. Tetrodotoxin abolished both the contractile response and the increase in ATP release resulting from intramural nerve stimulation. There was no increase in ATP release during contraction resulting from direct muscle stimulation following nerve paralysis with tetrodotoxin.4 Sympathectomy with 6-hydroxydopamine did not affect release of ATP in response to intramural nerve stimulation.5 Release of ATP was dependent on the concentration of calcium ion in the medium.6 Contractions in response to non-adrenergic, non-cholinergic intramural nerve stimulation were closely mimicked by ATP, but not by acetylcholine or histamine.7 Adenosine and dipyridamole reduced the contractions to both ATP and non-cholinergic nerve stimulation.8 2-2'-Pyridylisatogen was not a specific blocker of either ATP or intramural nerve stimulation in the guinea-pig bladder. 2-Substituted imidazolines initiated spontaneous activity making it impossible to assess any blocking action that they may have had.9 Prostaglandins (E(1), E(2) and F(2alpha)) gave weak, slow contractions and an increase in spontaneous activity. Both the response to ATP and non-adrenergic, non-cholinergic nerve stimulation were greatly potentiated in the presence of prostaglandins.10 In the presence of indomethacin the response to non-adrenergic, non-cholinergic nerve stimulation was virtually abolished following desensitization to ATP.
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PMID:Purinergic innervation of the guinea-pig urinary bladder. 2 86

Cardiotoxin isolated from Naja mossambica mossambica selectively deactivates the sodium-potassium activated adenosine triphosphatase of axonal membranes. Tetrodotoxin binding and acetylcholinesterase activities are unaffected by cardiotoxin treatment. The details of association of cardiotoxin with the axonal membrane were studied by following the deactivation of the sodium-potassium activated adenosine triphosphatase and by direct binding measurements with a tritiated derivative of the native cardiotoxin. The maximal binding capacity of the membrane is 42-50 nmol of cardiotoxin/mg of membrane protein. The high amount of binding suggests association of the toxin with the lipid phase of the membrane. It has been shown that cardiotoxin first associates rapidly and reversibly to membrane lipids, then, in a second step, it induces a rearrangement of the membrane structure which produces and irreversible deactivation of the sodium-potassium activated adenosine triphosphatase. Solubilization of the membrane-bound ATPase with Lubrol WX gives an active enzyme species that is resistant to cardiotoxin-induced deactivation. Cardiotoxin binding to the membrane is prevented by high concentrations of Ca 2+ and dibucaine. Although cardiotoxins and neurotoxins of cobra venom have large sequence homologies, their mode of action on membranes is very different. The cardiotoxin seems to bind to the lipid phase of the axonal membrane and inhibits the sodium-potassium activated adenosine triphosphatase, whereas the neurotoxin associates with a protein receptor in the post-synaptic membrane and blocks acetylcholine transmission.
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PMID:Molecular mechanism of cardiotoxin action on axonal membranes. 18 4

A vertical-type in vivo microdialysis probe and a sensitive, specific radioimmunoassay (RIA) were used to study the mechanism of acetylcholine (ACh) release in the striatum of anesthetized rats. Without the use of physostigmine, a cholinesterase inhibitor, our RIA could still detect the amount of ACh present in the perfusate (5.6 +/- 0.6 fmol/min, n = 16). Tetrodotoxin (1 microM) produced a significant decrease in the amount of ACh collected in the perfusate, suggesting that basal ACh determined under the present experimental conditions was related to cholinergic neural activity. Atropine (0.1-1 microM) applied topically via the dialysis probe did not affect the amount of ACh recovered in the perfusate in the absence of physostigmine. Addition of physostigmine (10 microM) to the perfusion fluid produced about a 100-fold increase in the amount of ACh collected. In the presence of physostigmine, topical administration of atropine and pirenzepine (0.01-1 microM) through a dialysis probe produced a further three- to fourfold increase in ACh output, whereas a slight increase was produced by AF-DX 116 at the highest concentration (1 microM). These results indicate that presynaptic modulation of ACh release in the striatum does not occur under basal conditions, and that presynaptic M1 muscarinic receptors are involved in the modulation of ACh release when the ACh concentration is raised under certain conditions.
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PMID:Determination of acetylcholine release in the striatum of anesthetized rats using in vivo microdialysis and a radioimmunoassay. 186 Nov 56

Electrolyte transport across two preparations of mucosa from rat colon descendens was compared to determine what influence the submucosal plexus has on electrolyte transport. One preparation consisted of the mucosa, muscularis mucosae, and the submucosal tissue and is referred to as the mucosa-submucosa preparation. The second preparation obtained by further blunt dissection of the mucosa-submucosa preparation consisted of only the mucosa and the circular muscle layer of muscularis mucosae and is referred to as the mucosa preparation. Histological studies showed that the submucosal tissue and the longitudinal layer of muscularis mucosae could be removed leaving only the mucosa and the circular layer of muscularis mucosae. The extensive neuronal network of the submucosa was shown when the submucosal tissue and longitudinal muscle layer of muscularis mucosae, which were removed, were stained histochemically for acetylcholinesterase activity. Both the mucosa-submucosa and mucosa preparations absorbed Na+ and Cl- when short-circuited. However, Na+ and Cl- absorption were significantly higher in the mucosa preparation. The increase in Na+ and Cl- transport in the mucosa preparation was accompanied with a decrease in the short-circuit current (Isc), the open-circuit potential difference (p.d.) and the transmural tissue conductance (Gt) when compared to the mucosa-submucosa preparation. Tetrodotoxin (TTX), a neurotoxin which blocks specifically the propagation of action potentials in excitable tissues, dose-dependently decreased Isc and p.d. in the mucosa-submucosa preparation when added to the serosal solution. The half-maximal effective concentration of TTX was 5 nM and maximal effective concentration 100 nM. TTX (1 microM) had no effect on Isc or p.d. when added to the mucosal solution. The decrease in Isc and p.d. caused by TTX in the mucosa-submucosa preparation was accompanied with an increase in Na+ and Cl- absorption. TTX caused only a small decrease in Isc and p.d. in the mucosa preparation. However, there was no measurable change in Na+ and Cl- transport in the mucosa preparation. The results suggest that spontaneously active neurones from the submucosal plexus have an inhibitory influence on the mucosa. Physical removal of the submucosal plexus or pharmacological blockade of the neurones within the mucosa-submucosa preparation by TTX led to enhanced absorption, suggesting that the set point of the mucosa for electrolyte transport is at or near a maximal absorptive state. Regulation or modulation of the mucosa may therefore occur by mechanisms that lower this set point, causing an inhibition of absorption of electrolytes.
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PMID:Submucosal plexus and electrolyte transport across rat colonic mucosa. 241 17

A radioisotope method has been developed for measuring the stimulation-evoked release of acetylcholine without the use of cholinesterase inhibitors from the mouse hemidiaphragm preparation which had been loaded with 3H-choline. Evidence has been obtained that 3H-choline was taken up by and released from both innervated and non-innervated mouse hemidiaphragm preparations. However, it was released in the form of 3H-acetylcholine in response to electrical field stimulation only from the innervated preparations. Long lasting (51 min) S1 stimulation of the preparations exhausted the radioactive acetylcholine stores to the extent that S2 did not evoke any release of 3H. These data suggest that when the labelled acetylcholine stores become exhausted, the labelled choline, still present in the tissue, cannot be released by electrical stimulation. Tetrodotoxin (1 mumol/l) administration and Ca withdrawal inhibited, 20-100 mumol/l 4-aminopyridine enhanced the release of 3H-acetylcholine in response to electrical stimulation. Activation of the presynaptic muscarinic receptors by the agonist oxotremorine (50 mumol/l) decreased the liberation of 3H-acetylcholine. The muscarinic antagonist atropine (1 mumol/l) abolished the inhibitory effect of oxotremorine and by itself increased the evoked release of the newly formed 3H-acetylcholine. Adenosine (50 mumol/l) reduced the evoked release of radioactivity. Theophylline (30 mumol/l) prevented the inhibitory effect of adenosine and itself enhanced the release. Xylazine (1 mumol/l), an alpha 2-adrenoceptor agonist did not affect the release. It is concluded that the stimulation-evoked release of 3H-acetylcholine from the mouse phrenic nerve hemidiaphragm preparation preloaded with 3H-choline is derived from the motor nerves. The release of acetylcholine is modulated by activation of presynaptic muscarinic and adenosine receptors.
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PMID:Modulation of stimulation-evoked release of newly formed acetylcholine from mouse hemidiaphragm preparation. 281 46

The reversible acetylcholinesterase inhibitor, physostigmine, stimulated in a dose-dependent manner the accumulation of [3H]inositol monophosphate ([3H]IP1) in lithium-treated neostriatal slices. The muscarinic agonists, carbachol and oxotremorine, also stimulated [3H]IP1 accumulation. Atropine completely blocked the physostigmine-induced accumulation but had no effect on the basal accumulation. Tetrodotoxin partially inhibited the physostigmine-induced [3H]IP1 accumulation but had no effect on the carbachol-induced accumulation. 4-Aminopyridine stimulated the basal [3H]IP1 accumulation and potentiated the physostigmine-induced accumulation. This potentiation was blocked by tetrodotoxin. The physostigmine dose-response curve for the stimulation of [3H]IP1 accumulation was similar to its dose-response curve to inhibit acetylcholinesterase activity in the neostriatum. The results suggest that, under our experimental conditions, the acetylcholine released spontaneously from intrinsic cholinergic neurons does not activate the striatal muscarinic receptors coupled to phosphoinositide breakdown unless the intrinsic acetylcholinesterases are inhibited.
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PMID:Physostigmine stimulates phosphoinositide breakdown in the rat neostriatum. 285 73

Acetylcholinesterase staining and studies on the uptake of [3H]choline into the subsequent efflux of tritium from collicular slices were carried out in order to provide evidence for a neurotransmitter function of acetylcholine in rabbit superior colliculus. Acetylcholinesterase staining was dense and homogeneous in superficial layers whereas the staining was arranged in patches with slightly higher density caudally than rostrally in the intermediate layers. The accumulation of tritium in slices incubated with [3H]choline depended on time, temperature and concentration, and was inhibited by hemicholinium-3. Accumulation was slightly higher in caudal than in rostral slices. Electrical stimulation enhanced tritium outflow from slices preincubated with [3H]choline. Tetrodotoxin and a low calcium medium inhibited the evoked overflow whereas hemicholinium-3 caused an enhancement. Oxotremorine decreased the evoked overflow; atropine prevented this effect. The opioids [D-Ala2, MePhe4, Glycol5]enkephalin, [D-Ala2, D-Leu5]enkephalin and ethylketocyclazocine caused an inhibition. The effects of the latter two agonists were antagonized by naloxone. The GABAB-receptor-agonist (-)-baclofen decreased the evoked overflow at lower concentrations than GABA, whereas the GABAA-receptor-agonist muscimol was ineffective. Serotonin produced an inhibition which was prevented by metitepin, alpha- and beta-adrenoceptor as well as dopamine-receptor ligands caused no change. It is concluded that in the rabbit superior colliculus the pattern of acetylcholinesterase staining is comparable, but not identical to the distribution in other species. The accumulation of [3H]choline, as well as the tetrodotoxin-sensitive and calcium-dependent overflow of tritium upon electrical stimulation (reflecting presumably release of [3H]acetylcholine) indicate that acetylcholine has a neurotransmitter function in this tissue. The release of [3H]acetylcholine was modulated by various transmitter substances and related compounds. The pattern of modulation of release differed from the pattern in other cholinergically innervated tissues.
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PMID:Evidence for a neurotransmitter function of acetylcholine in rabbit superior colliculus. 289 96

1. Studies of the synthesis and release of radioactive acetylcholine in rat brain-cortex slices incubated in Locke-bicarbonate-[U-(14)C]glucose media, containing paraoxon as cholinesterase inhibitor, revealed the following phenomena: (a) dependence of K(+)-or protoveratrine-stimulated acetylcholine synthesis and release on the presence of Na(+) and Ca(2+) in the incubation medium, (b) enhanced release of radioactive acetylcholine by substances that promote depolarization at the nerve cell membrane (e.g. high K(+), ouabain, protoveratrine, sodium l-glutamate, high concentration of acetylcholine), (c) failure of acetylcholine synthesis to keep pace with acetylcholine release under certain conditions (e.g. the presence of ouabain or lack of Na(+)). 2. Stimulation by K(+) of radioactive acetylcholine synthesis was directly proportional to the external concentration of Na(+), but some synthesis and release of radioactive acetylcholine occurred in the absence of Na(+) as well as in the absence of Ca(2+). 3. The Na(+) dependence of K(+)-stimulated acetylcholine synthesis was partly due to suppression of choline transport, as addition of small concentrations of choline partly neutralized the effect of Na(+) lack, and partly due to the suppression of the activity of the Na(+) pump. 4. Protoveratrine caused a greatly increased release of radioactive acetylcholine without stimulating total radioactive acetylcholine synthesis. Protoveratrine was ineffective in the absence of Ca(2+) from the incubation medium. It completely blocked K(+) stimulation of acetylcholine synthesis and release. 5. Tetrodotoxin abolished the effects of protoveratrine on acetylcholine release. It had blocking effects (partial or complete) on the action of high K(+), sodium l-glutamate and lack of Ca(2+) on acetylcholine synthesis and release. 6. Unlabelled exogenous acetylcholine did not diminish the content of labelled tissue acetylcholine, derived from labelled glucose, suggesting that no exchange with vesicular acetylcholine took place. In the presence of 4mm-KCl it caused some increase in the release of labelled acetylcholine. 7. The barbiturates (Amytal, pentothal), whilst having no significant effects on labelled acetylcholine synthesis in unstimulated brain except at high concentration (1mm), diminished or abolished (at 0.25 or 0.5mm) the enhanced release of acetylcholine, due to high K(+) or lack of Ca(2+). The fall in tissue content of acetylcholine, due to lack of Ca(2+), was diminished or abolished by pentothal (0.25 or 0.5mm) or Amytal (0.25mm).
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PMID:Control of synthesis and release of radioactive acetylcholine in brain slices from the rat. Effects of neurotropic drugs. 472 96

1. Cortical slices from rat brain were incubated in media containing the irreversible cholinesterase inhibitor soman and a high KCl concentration, and the release and synthesis of acetylcholine (ACh) were determined.2. Atropine enhanced the release and synthesis of ACh.3. Tetrodotoxin, a substance which blocks nervous conduction, did not influence the release and synthesis of ACh, in the absence or in the presence of atropine. Therefore the nerve endings are probably the site at which atropine acts when stimulating the release and synthesis of ACh.4. Pretreatment of the slices with botulinum type A toxin partially blocked the release and synthesis of ACh and reduced the extra amounts of ACh released and synthesized under the influence of atropine.5. Lowering the calcium or raising the magnesium concentration in the incubation medium reduced the release and synthesis of ACh and their enhancement by atropine.6. Physostigmine decreased the total extractable ACh content of the slices during incubation in a 25 mM KCl containing medium. This decrease was nearly prevented when the release and synthesis of ACh were inhibited by omission of the calcium ions from the medium, but was enhanced by atropine.7. The observations made with pretreatment by botulinum type A toxin, with changes in the calcium and magnesium concentration as well as with physostigmine, all support the theory that it is primarily the release of ACh which is enhanced by atropine and that its stimulating action on the synthesis results from the increased release.
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PMID:Stimulation by atropine of acetylcholine release and synthesis in cortical slices from rat brain. 549 92


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