Acetylcholine Formation Research Articles

Non-enzymatic imidazole-catalysed acyl transfer reaction and acetylcholine synthesis.

On the basis of detailed kinetic and inhibitory studies of the enzyme choline acetyltransferase, White and Cavallito have proposed that a catalytic imidazole group is involved in the acyl transfer reaction1. Their studies and those of others2 have also shown that imidazole seems to stimulate the enzymatic synthesis of acetylcholine (ACh) from acetyl-CoA and choline. This stimulation was dependent on the presence of the enzyme preparation and non-enzymatic formation of ACh was not observed1, 2.

Increased activity of the peripheral sympathetic nervous system: induction of choline acetyltransferase in the preganglionic cholinergic neurone.

PROLONGED increase in the activity of the peripheral sympathetic nervous system leads to augmented synthesis of tyrosine hydroxylase (E.C. 1.14.3.a) and dopamine β-hydroxylase (E.C. 1.14.2.1) in the terminal adrenergic neurone1–6. As the induction of these key enzymes in the synthesis of the adrenergic transmitter norepinephrine is mediated by increased activity of the preganglionic cholinergic nerves2, the question arises, is the augmented utilization of acetylcholine also accompanied by increased synthesis of choline acetyltransferase (E.C. 2.3.1.6), the enzyme which is responsible for the formation of acetylcholine ?

Choline: high-affinity uptake by rat brain synaptosomes.

Synaptosomes from rat brain accumulate choline by two kinetically distinct processes, a high-affinity uptake system [Michaelis constant (K(m)) = 1 x 10(-6)M], and a low-affinity system (K(m) = 9 x 10(-5)M). The high-affinity uptake system requires sodium, and is associated with considerable formation of acetylcholine. The low-affinity uptake system is less dependent on sodium, and does not appear to be associated with a marked degree of acetylcholine formation. The high-affinity choline uptake appears to represent selective choline accumulation by cholinergic neurons.

Acetylcholine formation in mouse brain and effect of cholinergic drugs.

TREATMENT of mice with arecoline or oxotremorine produces tremors accompanied by a transient increase in the brain level of acetylcholine lasting for 20 to 30 min1. We reported that administration of pilocarpine, whose peripheral cholinomimetic effects resemble those of arecoline, also markedly increases the level of brain acetylcholine in rats2,3. By contrast with other cholinomimetics, however, the pilocarpine-induced increase in acetylcholine lasts for several hours and is not accompanied by tremors. These findings suggest that arecoline and pilocarpine increase brain acetylcholine levels by different mechanisms. This study compares the effects of arecoline and pilocarpine administration on the conversion of choline-3H to acetylcholine-3H to elucidate the mechanism by which these drugs raise the brain acetylcholine level.

Acetylcholine metabolism peculiarities in aging

In experiments on 1, 8–10 and 26–28 months old white rats there were determined: the intensity of acetylcholine formation in isolated atria (Vlk and Tuček, 1964); choline acetylase (EC 2.3.1.6.) activity (Hebb and Waites, 1956; Tuček, 1964) in heart, sciatic nerve and m.gastrocnemius; acetylcholinesterase (EC 3.1.1.7.) and non specific cholinesterase (EC 3.1.1.8.) activity (Vlk and Tuček, 1961) in heart, m.gastrocnemius and intestine. The intentine of acetylcholine formation in isolated atria was decreased with aging. Choline acetylase activity in atria and sciatic nerve was increased at the period of growth but in old rats it was significantly decreased. A considerable drop of choline acetylase activity was found in skeletal muscle of adult rats as compared with 1 month old animals. It remained unchanged in the muscles of old rats. With aging the intensity of acetylcholine hydrolysis decreased in the variuus parts of the heart and skeletal muscle, but did not change in intestine. In atria of old rats, the activity of the non specific cardiac cholinesterase rats was at the same high level as in adults, while in the other parts of heart its activity was gradually decreased with aging. The activity of the skeletal muscles acetylcholinesterase was decreased with aging. Age-conditioned changes in acetylcholine metabolism play an important role in weakening nervous influences upon the tissues and increase their sensitivity to the humoral factors in aging.

Effects of oxotremorine on brain acetylcholine formation in vivo and in vitro

Under our experimental conditions rat brain normally contains 14.4 ± 1.3 ( M ± SD) m μmole acetylcholine (AcCh)/g. If oxotremorine (OT), 2 mg/kg body wt. i.p., is given to rats, this increases the level of AcCh to 22.1 ± 2.3. Homogenates of rat brain left for 15 min at 20° in the presence of physostigmine salicylate (10 −5 M) contain 13·5 ± 1·4 ( M ± SD) m μmole AcCh/g tissue. OT (10 −5 M) added to the homogenate increases the AcCh level to 20·9 ± 3·4/ g tissue. Addition of 5–8 m μmole AcCh/g tissue to a homogenate of normal rat brain followed by hydrolysis of the free acetylcholine before incubation has no inhibitory effect on the formation of AcCh produced by OT in vitro. The ability of OT to increase the AcCh level in a brain homogenate from rats pretreated with OT seems to be inversely proportional to its effect in vivo. The amount of AcCh produced by OT either in vivo or in vitro does not exceed a certain limit. In combined experiments mirror-like time curves for the concentration of AcCh are obtained. This observation suggests that OT has a similar mechanism of action in vivo and in vitro. The possibility for the presented results to be reconciled with an increased biosynthesis of AcCh has been discussed.

A sensitive radiochemical assay for choline acetylase

A sensitive radiochemical assay for choline acetylase has been devised based on the formation of acetylcholine from tritium-labeled acetate. The acetylcholine is separated from other labeled components by chromatography on a short column of Amberlite CG-50 ion exchanger. The procedure is sufficiently specific and sensitive so that it can be used for the measurement of the acetylase in crude, unfractionated homogenates of brain.

Effects of quaternary bases and inorganic cations on acetylcholine synthesis in nervous tissue.

A number of quaternary bases were tested for their ability to inhibit the synthesis of acetylcholine (ACh) by incubated minced mouse brain. Tetramethyl-, tetraethyl-, tetrapropyl-, and tetrabutyl-ammonium were moderately active as inhibitors, the strongest being the tetraethyl base (TEA), which was 1–2% as active as the hemicholinium HC-3. Weaker activity was exhibited by hexamethonium, d-tubocurarine, and tolazoline; NH4Cl and N-methylnicotinamide were inactive at concentrations up to 10−2 M. Except in high concentrations, none of the bases significantly affected the release of ACh from the tissue into the eserinized medium. The addition of choline to the medium somewhat increased the rate of ACh formation when the bases were absent and strikingly antagonized the inhibitory action of HC-3 and TEA. TEA also resembled HC-3 in that (i) it reduced the ACh content of the preganglionically excited superior cervical ganglion of the cat, though neither stimulation alone nor the drug alone has such an effect; (ii) it killed mice by paralyzing respiration, and this effect was antagonized by choline; (iii) its inhibitory effect on ACh synthesis by intact nervous tissue was not due to direct inhibition of choline acetylase. The finding of Birks and Quastel that extracellular Na+is essential for the synthesis and storage of ACh by perfused sympathetic ganglia was confirmed for incubated brain tissue. Neither the action of HC-3 and TEA in inhibiting ACh synthesis, nor that of Na+in promoting it, has as yet been clarified.

Biosynthesis of acetyl- l-carnityl choline

Earlier work had shown that acetyl-1-carnityl CoA was the material with acetylcholine-like activity which accumulated in the brain of narcotized rats. Accordingly, it was of importance to determine what normal function this material could have in the body. It appeared likely to be involved in acetylcholine and/or acetyl-1-carnityl choline formation. Since both these products are choline esters and it has been shown that the enzyme choline acetyltransferase is nonspecific for the esterification of choline, we have used the acetyl-1-carnityl CoA from narcotized brain extracts to determine which of these two products is produced when this substance is reacted with an extract of rat brain acetone powder as source of enzyme and choline. It was found that acetyl-1-carnityl choline could have been the only product formed under the particular reaction conditions studied. Product formation was indicated by increased acetylcholine-like activity as determined by bioassay. Acetylcholine formation could not be demonstrated with the particular reaction studied. These results also provide further evidence that the material with acetylcholine-like activity present in brain extracts from narcotized rats was not acetylcholine.

ACETYLCHOLINE FORMATION IN LOBSTER SENSORY AXONS.

Abstract 1. 1. The concentration of choline acetylase (acetyl-CoA: choline O-acetyltransferase, EC 2.3.1.6) in the nerve fibers of the walking leg of the lobster has been determined. In sensory bundles, dissected from the whole nerve trunk, the activity of the enzyme was found to be on the average 2 μm/g wet wt./h; the values of the whole nerve' trunk were similar. 2. 2. The sensory bundle is formed by approx. 800 axons, each about 5 μ in diameter, estimated on the basis of photomicrographs; the total surface area per g nerve is therefore approx. 400 cm2. Referred to cm3/sec the enzyme activity amounts to 1.5·10−6 μm of acetylcholine formed. 3. 3. Recent information on the concentration of acetylcholinesterase (acetylcholine acetyl-hydrolase, EC 3.1.1.7) in lobster nerves per unit time and surface area permits an estimate of the amount of acetylcholine which may be hydrolyzed per cm2. On this basis the amount of acetylcholine formed in the sensory axons would be adequate for more than 400 000 impulses/h. 4. 4. The objection was raised to the proposal role of acetylcholine in conduction, that the concentration of choline acetylase in sensory fibers is too low to be compatible with the theory. This difficulty has now been eliminated.

L-METHIONINE AS A MODULATOR OF ATRIAL RHYTHMICITY IN RABBIT AND GUINEA-PIG

By using the intracellular microelectrode technique, Toda (1) reported the effects of adrenaline, noradrenaline and reserpine on transmembrane potentials in pacemaker and non-pacemaker fibers of isolated rabbit atria, and suggested that endogenously liberated adrenaline and noradrenaline play an important physiological role in initiating and maintaining atrial rhythmicity. Further studies on cardiac mechanism were done by Matsuo and Tachi (2) who suggested that the initiating substance in atrial contraction may be adrenaline or noradrenaline in isolated atrial preparation. On the other hand, Bulbring and Burn (3, 4) concluded that the local formation of acetylcholine initiates auricular contraction. Kottegoda (5) also reported that acetylcholine in a high concentrations had a stimulant action on rabbit atria in the presence of atropine. In rabbit auricles, noradrenaline and acetylcholine were found present in about the same amounts of 1.3 to 1.48 μg/g [Burn (4), Matsuo (6)]. From these observations it may safely be assumed that endogenous acetylcholine is the trigger substance in the release of endogenous adrenaline or noradrenaline which, in turn, initiates atrial movement. Conversely, the depletion of endogenous acetylcholine or noradrenaline in atria may cause the arrest of atrial movement. Paasonen and Krayer (7) have shown that the administration of reserpine to a dog heart-lung preparation leads to a marked decrease in the noradrenaline content of the heart, but the adrenaline content normally 5 per cent that of noradrenaline shows no clear-cut decrease. This result would indicate that, rather than noradrenaline, endogenous adrenaline may be the more important hormone relative to atrial movement. Kirshner and Goodall (8) have shown that the soluble fraction of adrenal medullary hon ogenates form adrenaline from noradrenaline and L-methionine in the presence of ATP. Pilgeram et al. (9) suggested that the methyl groups of choline may be derived by transmethylation from L-methionine, and that the active formation of phospholipid choline from aminoethanol was obtained only through utilization of the methyl group of L-methionine. It may therefore be assumed that L-methionine is the substance essential both to endogenous adrenaline and acetylchholine, which are the initiators and modulators of atrial rhythmicity. The present experiment was carried out to study the effects of L-methionine on isolated normal, or reserpine or nicotine-treated atria, in order to discover the physiological role of L-methionine in the cardiac mechanism.

The effect of lipocaic on the cholinergic reaction of the blood in dogs undergoing partial pancreatectomy

From analysis of the results obtained it may be concluded that lipocaic is able to a considerable degree to prevent those disturbances of acetylcholine formation which as a rule are found at certain postoperative periods in depancreatized animals. The main cause of these disturbances is consequently a deficiency of this hormone. This suggests that the pancreatic hormone, lipocaic, plays a part in the control of the synthesis of acetylcholine, one of the most important mediators of the nervous system. The results which we obtained are of obvious interest in the evaluation of the action of lipocaic in clinical con

The Mechanism of Action of the Hemicholiniums

Publisher Summary Hemicholiniums are capable of affecting cholinergic transmission at a variety of sites in an apparently unique fashion and therefore represent a new tool in the investigation of cholinergic mechanisms. HC-3 is studied primarily with reference to the neuromuscular junction, autonomic ganglia, postganglionic parasympathetic endings, and central nervous system. It blocks effectively at all cholinergic sites studied in the chapter but only when the synapses involved are forced to transmit at high frequency. The primary actions of the drug (i.e., those observed at lowest effective doses) involve a pre-synaptic depressant effect resulting from decreased acetylcholine formation. Its effect in this latter regard is not upon the acetylation phase of acetylcholine synthesis but upon some process involved in the acquisition of choline by nerve cells. Choline is a specific and dramatic antidote for HC-3 poisoning. Physostigmine also antidotes HC-3 toxicity but to a lesser degree.

Action of Ganglion Blocking Drugs on Choline Acetylase

THE first practical hypotensive drugs which acted by causing autonomic ganglionic block were bis-quaternary ammonium salts; recently, substances containing only a single secondary or tertiary amine group have been introduced as hypotensive agents of a similar type. There are, however, differences in the details of the pharmacological actions of the two types of drugs; for example, the mono-amine compounds, mecamylamine and pempidine, are slower in onset of action but more prolonged when compared with the older group (for example, hexamethonium or pentolinium). The bis-quaternary ammonium drugs paralyse ganglia by extracellular competition with acetylcholine for synaptic receptor sites; the differences in action might be explicable if the newer compounds acted in some other way, for example, by inhibition of acetylcholine formation. Their ability to penetrate cell lipid membranes or barriers makes such an intracellular action plausible.

モルモット腸管運動及びAcetylcholine樣物質生成に及ぼす諸種代謝物質の影響

モルモット腸管運動及びAcetylcholine樣物質生成に及ぼす諸種代謝物質の影響

Tetanized single contractions of a neuromuscular frog preparation after pancreatectomy

Ablation of pancreas in frogs causes development of single tentanized contractions more rapidly and better expressed than in control experiments on the fifth and the ninth day after operation. This may be accounted for by a decrease in lability of the nervous trunk and intensification of after-excitatory processes. The effects of ablation of pancreas are apparently due to an impediment in formation of acetylcholine in the tissues.

The formation of acetylcholine in the heart; its effect on the systemic output and its importance for auricular fibrillation caused by aconitine.

The Journal of PhysiologyVolume 131, Issue 2 p. 317-328 ArticleFree Access The formation of acetylcholine in the heart; its effect on the systemic output and its importance for auricular fibrillation caused by aconitine J. H. Burn, J. H. BurnSearch for more papers by this authorE. M. Vaughan Williams, E. M. Vaughan WilliamsSearch for more papers by this authorJ. M. Walker, J. M. WalkerSearch for more papers by this author J. H. Burn, J. H. BurnSearch for more papers by this authorE. M. Vaughan Williams, E. M. Vaughan WilliamsSearch for more papers by this authorJ. M. Walker, J. M. WalkerSearch for more papers by this author First published: 28 February 1956 https://doi.org/10.1113/jphysiol.1956.sp005465Citations: 15AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume131, Issue2February 28, 1956Pages 317-328 RelatedInformation

Emotional and psychological factors in epilepsy: physiological background.

1. An elementary seizure discharge is characterized by high amplitude, synchronized activity expressed by interlocking brain wave rhythms of different frequencies. Among various components of the electrical changes associated with convulsions, slow waves of polarization may play an important role during both ictal and postictal stages. 2. Rhinencephalic structures show the lowest threshold. Their epileptic discharges show the most intricate organization. Traveling slow waves of polarization are very easy to induce in the olfactory brain, particularly in the Ammon's Formation. Contrasting with the complexity and intensity of the electrical correlates of the seizure discharges, there is a meagerness of its "clinical" expression in animals in terms of motor activity. Awareness is impaired and certain manifestations of emotional disturbances are reported. Experiments with ablation and chemical stimulation confirm the role of the rhinencephalon in emotional control. Experiments with sensory stimulation which reveal a high level of intergration also show an unusual reaction of hypersynchronization under certain conditions. 3. An epileptogenic excitation of a limited extent may produce psychological manifestations by a dual mechanism: ( a) Only partial decrease of awareness may be experienced by the patient as a threat of ego dissolution and thus stir his emotional reactions. ( b) The involvement of certain specific areas ( for instance the rhinencephalon) may be expressed by disturbances of the emotional control. 4. Emotional stimuli may induce a convulsion through either ( a) a creation of a general excitatory state with an excessive formation of either acetylcholine or insulin; or ( b) a preliminary conditioning of certain stimuli which Set up epileptogenic states in those areas of the brain which participate in the control of emotional processes ("affectogenic" epilepsy).

大腦組織のAcetylcholine生成

The relation of the acetylcholine (ACh) formation to the pyruvate metabolism in rat brain tissue was studied. When choline and choline acetylase preparation (CHA) coexisted with the pyruvate metabolism by cyclophorase system (GYP) of rat brain (CHA-CYP-Pyruvate system), the large amount of ACh was produced under the aerobic condition, while negligible under the anaerobic condition. Aerobic formation of ACh was greatly decreased, accompanied by a marked rise of O2-uptake by the addition of 2, 4-dinitrophenol to CHA-CYP-Pyruvate system or to brain slices, while only slightly depressed with CHA-ATP-Acetate system. ACh formation in CHA-CYP-Pyruvate system was considerably accelerated by the addition of CoA, adenylic acid and cysteine, whereas slightly increased with magnesium and coenzyme 1. ACh formation in the brain tissue is likely to be enhanced by some mechanism closely related to the respiratory system, especially to the oxidative phosphorylation coupled with it.

III. Experiments for Demonstrating the Possible Formation of Acetylcholine In the Perilymph and in the Endolymph In Response to Sound Stimulation Of The Ear Perilymph

III. Experiments for Demonstrating the Possible Formation of Acetylcholine In the Perilymph and in the Endolymph In Response to Sound Stimulation Of The Ear Perilymph