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... As early as 1867, Adolf von Baeyer chemically synthesized ACh, but it was then left for nearly four decades without exploration of its biological activity . In 1906, Hunt and Taveau  discovered the extraordinary strong hypotensive action of ACh in rabbits during their study of the physiological actions of choline derivatives. ...
Acetylcholine (Ach) is an excitatory neurotransmitter formed from choline and acetic acid through the process of esterification. It is the primary neurotransmitter in the parasympathetic autonomic nervous system, a chemical transmitter at the neuromuscular junction, and a neuromodulator in the brain. This chapter outlines the history, neurochemical profile, receptor functioning, metabolism, pharmacological importance, and the clinical application of Ach.KeywordsAcetylcholineCholinergic transmissionParasympathomimeticNeurotransmitter
Reinecke salt-precipitable material from trichloroacetic acid extracts of calf brain was divided into two parts. One part was separated by paper chromatography and the material eluted from particular zones was converted to the respective tetrachloroaurate derivative. Acetylcholine was isolated from the other part of the extract following the original procedure of Stedman and Stedman. In both parts of the experiment, the materials as their tetrachloroaurate derivatives were identified by their melting point and mixed melting point. It was observed that in addition to acetylcholine, calf brain extracts contains relatively large amounts of butyryl choline and of acetyl-l-carnitine. This is the first report of the presence of acetyl-l-carnitine in tissue extracts. Lesser amounts of other betaine esters were also found in these extracts.
The isolated perfused cat heart was used to study the synthesis of tritiated acetylcholine from choline-methyl-H3. Evidence for the synthesis of acetylcholine was provided by the chromatographic separation of a compound having the same Rf value as authentic acetylcholine in two different solvent systems and by an isotope dilution analysis. The rate of synthesis of tritiated acetylcholine in the right ventricle and papillary muscles increased with increasing substrate concentrations. Isolated perfused cat hearts with the right vagus nerve intact were used to determine if vagal stimulation was capable of releasing the tritiated acetylcholine formed. A significant increase in the rate of release of tritiated acetylcholine was associated with a decrease in heart rate during vagal stimulation. It is concluded that the tritiated acetylcholine synthesized by the isolated perfused cat heart is associated with its vagal innervation.
1. Three forms of acetylcholine occur in subcellular fractions of brain tissue: free acetylcholine, present in the high-speed supernatant from eserinized sucrose homogenates; stable bound acetylcholine, present in synaptic vesicles; and labile bound acetylcholine, present in the cytoplasm of synaptosomes (detached presynaptic nerve terminals). 2. The relationship between these forms has been investigated by isolating the subcellular fractions from the cortical tissue of cats and guinea pigs excised 1hr. after infiltration of [N-Me-(3)H]choline into the cortex in vivo. 3. Since choline is a ubiquitous metabolite, means were devised for isolating the radioactive acetylcholine on columns of the weak acid ion-exchange resin IRF-97; control experiments with samples of extracts treated with acetylcholinesterase showed that the radioactivity attributed to acetylcholine migrated to the choline peak after cholinesterase treatment. 4. The specific radioactivities of the various forms of acetylcholine were different: labile bound (synaptosomal cytoplasmic) acetylcholine had the highest, stable bound (vesicular) acetylcholine the next highest, and the high-speed-supernatant form the lowest. 5. It is concluded that the various forms of acetylcholine could not have arisen during fractionation from a single pre-existing pool of acetylcholine.
Choline-methyl-H3 was employed in experiments in the cat in an attempt to label cerebral cortical stores of acetylcholine. Both Chromatographic and isotope dilution analysis established the presence and identity of labeled acetylcholine in extracts of unfractionated cerebral cortex as well as an undoubtedly crude mitochondrial fraction of this tissue after the intracerebral injection of tritium labeled choline. The radioactivity in this fraction was significantly reduced when hemicholinium No. 3 was injected into the cerebral cortex prior to the injection of tritiated eholine. The synthesis of labeled acetylcholine in the brain also was confirmed after intracerebral injection of tritiated choline in the young chick.The synthesisin vitro of tritiated acetylcholine from choline-methyl-H3 by cerebral cortical homogenates of the cat was demonstrated. No synthesis of labeled acetylcholine could be detected when the homogenates were incubated with electric eel acetylcholinesterase. The possibility of nonenzymatic conversion of labeled choline to its acetyl esterin vivo seems highly unlikely since significant conversion did not occurin vitro under conditions that simulated thosein vivo.
1. Surplus acetylcholine (ACh) is the extra ACh that accumulates in cholinergic nerve endings when they are exposed to an anticholinesterase agent. The synthesis and turnover of this ACh was examined in the cat's superior cervical ganglion.2. Surplus ACh did not accumulate in chronically decentralized ganglia perfused with eserine-choline-Locke solution, and this shows that it is stored in presynaptic nerve terminals.3. Surplus ACh accumulated more rapidly in ganglia perfused with eserine than in ganglia perfused with neostigmine or with ambenonium; accumulation was delayed by 45-60 min when a quaternary anticholinesterase was used. However, the release of ACh upon preganglionic nerve stimulation was the same during perfusion with eserine, neostigmine or ambenonium. It is concluded that intracellular acetylcholinesterase normally destroys surplus ACh, whereas extracellular enzyme destroys released ACh.4. When ganglia were perfused with [(3)H]choline and eserine, the surplus ACh that accumulated was labelled but its specific radioactivity was only 38% of that of the choline added to the perfusion fluid.5. Surplus ACh was not released by nerve stimulation and was not mobilized for release during, or after, prolonged nerve stimulation. It is concluded that ACh released by nerve impulses is replaced by synthesis at the site of ACh storage and not by movement of ACh from the surplus pool.6. The accumulation of surplus ACh no more than doubled the total ACh content of ganglia, but turnover of ACh continued when the total amount was constant. Surplus ACh may contribute to spontaneous ACh output from eserinized preparations.7. When ganglia were perfused with a medium containing high K(+) (56 mM), surplus ACh was released.
Die hier behandelten Kohlensäurederivate und tierischen Basen berücksichtigen nur solche Verbindungen, die im Tierorganismus oder seinen Ausscheidungen nachgewiesen sind, also auch jene, die ihren Ursprung der Darmflora verdanken. Basen, die nur in vitro durch Bakterien oder deren Fermente entstanden oder bislang ausschließlich bei Pflanzen beobachtet sind, werden nicht erwähnt. Eine ausführliche fbersicht darüber findet sich bei GUGGENHEIM1 Bei den Basen mit unbekannter Konstitution sind ältere, die nur als Goldsalze abgetrennt wurden, ausgelassen, da die Trennung erfahrungsmäßig (s. unten) unvollständig ist und Gemische von Chlorauraten vorliegen können. Die Existenz der noch mit aufgeführten Basen Mirgelin und Kreatosin ist daher zweifelhaft.
When cortical slices are incubated with adenine-(14)C, adenine nucleotides are labeled in a small and relatively stable pool. The ATP-(14)C of this pool is readily converted to cAMP-(14)C during incubations with depolarizing agents, such as K(+), ouabain, veratridine, or batrachotoxin. During incubations with these agents, release of acetylcholine and of adenosine into the medium is enhanced. The increase in release of adenosine parallels the enhanced formation of cAMP-(14)C elicited by depolarizing agents, providing further evidence that adenosine may serve to couple electrical activity in the central nervous system with formation of cAMP. When adenosine or a depolarizing agent are incubated, together with a biogenic amine, such as histamine, serotonin, or norepinephrine, the combined effect on cAMP-(14)C formation in cortical slices is much more than additive. Extracellular levels of biogenic amines could in this manner modulate cAMP formation and biochemical responses in nervous tissue during electrical activity.
A method for the determination of ACh in tissues and subcellular fractions is described. The ACh is extracted by an ion pair exchange method, purified by paper chromatography and determined by enzymatic phosphorylation with choline kinase after enzymatic hydrolysis with AChE.
Die Frage, ob das normale Blut chemisch nachweisbares Acetylcholin enthlt, ist zu verneinen. In dem aus Blut dargestellten Reineckat fanden sich Cholin und geringe Mengen von Kreatinin in Form ihrer Reineckeverbindungen. Niemals konnte aus dem Blut-Reineckat das Acetylcholingoldsalz gewonnen werden. In diesem Punkte decken sich unsere Ergebnisse mit denen der vorangehenden pharmakologischen Untersuchungen, bei denen im Blute nur Cholin, niemals Acetylcholin gefunden wurde.Fr die Durchfhrung der Mikroelementaranalysen mchten wir Herrn Dr. Unterzaucher, Leiter der mikroanalytischen Abteilung am Organisch-Chemischen Institut von Herrn Geh. Rat Prof. Dr. H. Fischer, unseren ergebenen Dank zum Ausdruck bringen, ebenso Herrn Prof. Dr. Steinmetz fr die kristallographische Untersuchung der Goldsalze.
—1A procedure has been developed to measure ACh synthesis from [14C]-precursors. As little as 10−9 moles of ACh were detected as the result of de nova synthesis. Following incubation of cortex slices of rat brain with eserine and a tagged metabolite, ACh carrier was added to the incubation medium and to an extract from the slices. ACh was purified by chromatography on Amberlite CG-50, precipitation and recrystallization of ACh chloroaurate.2[U−14C]glucose and [2−14C]pyruvate formed similar amounts of [14C]ACh. Hydrolysis of ACh with subsequent chromatography of the resultant acetic acid demonstrated that all of the label was located in the acetyl moiety. [14C]acetate did not serve as a precursor of the acetyl group of ACh. Equivalent incorporation of carbons 1 and 6 of glucose into ACh indicated that glucose metabolism to ACh occurred via the Embden-Meyerhof pathway.3The amount of ACh detected by bioassay after incubation of cortex slices with [U−14C]glucose was approximately the same as that calculated as labelled ACh; this demonstrates that all of the acetyl groups of ACh formed during incubation were derived from glucose.4[14C]choline, either methyl or chain labelled, formed [14C]ACh while labelled ethanolamine, serine and methionine did not. Synthesis from labelled choline did not occur in the absence of glucose.5When both [U−14C]glucose and [14C]choline were incubated with brain slices, the acetyl and choline moieties of ACh were equally labelled; this demonstrates that the entire molecule was formed from added precursors. Slices supported a high rate of ACh synthesis without addition of choline. The addition of 10−4m-hemicholinium-3 inhibited ACh formation by more than 90 per cent from either [U-14C]glucose or [Me-14C]choline.6Study of the time course of ACh synthesis from glucose demonstrated a rapid formation of [14C]ACh within the slices which reached a maximum during the first hour of incubation. [14C]ACh in the incubation medium accumulated at a linear rate for 3 hr. Replacement of a portion of the sodium chloride of the incubation medium by potassium chloride to a final concentration of 31 mm-KCI markedly increased the formation of [14C]ACh found in the incubation medium. Decreased amounts of [14C]ACh were extracted from the slices by homogenization or by subsequent heating at pH 4 in the high potassium ion medium.
Genetic, biochemical, physiological, and pharmacological approaches have advanced our understanding of cholinergic biology for over 100 years. High-affinity choline uptake (HACU) was one of the last features of cholinergic signaling to be defined at a molecular level, achieved through the cloning of the choline transporter (CHT, SLC5A7). In retrospect, the molecular era of CHT studies initiated with the identification of hemicholinium-3 (HC-3), a potent, competitive CHT antagonist, though it would take another 30 years before HC-3, in radiolabeled form, was used by Joseph Coyle's laboratory to identify and monitor the dynamics of CHT proteins. Though HC-3 studies provided important insights into CHT distribution and regulation, another 15 years would pass before the structure of CHT genes and proteins were identified, a full decade after the cloning of most other neurotransmitter-associated transporters. The availability of CHT gene and protein probes propelled the development of cell and animal models as well as efforts to gain insights into how human CHT gene variation affects the risk for brain and neuromuscular disorders. Most recently, our group has pursued a broadening of CHT pharmacology, elucidating novel chemical structures that may serve to advance cholinergic diagnostics and medication development. Here we provide a short review of the transformation that has occurred in HACU research and how such advances may promote the development of novel therapeutics.
Acetylcholine was the first neurotransmitter identified and ATP is the hitherto final compound added to the list of small molecule neurotransmitters. Despite the wealth of evidence assigning a signaling role to extracellular ATP and other nucleotides in neural and non-neural tissues, the significance of this signaling pathway was accepted very reluctantly. In view of this, this short commentary contrasts the principal molecular and functional components of the cholinergic signaling pathway with those of ATP and other nucleotides. It highlights pathways of their discovery and analyses tissue distribution, synthesis, uptake, vesicular storage, receptors, release, extracellular hydrolysis as well as pathophysiological significance. There are differences but also striking similarities. Comparable to ACh, ATP is taken up and stored in synaptic vesicles, released in a Ca(2+)-dependent manner, acts on nearby ligand-gated or metabotropic receptors and is hydrolyzed extracellularly. ATP and acetylcholine are also costored and coreleased. In addition, ATP is coreleased from biogenic amine storing nerve terminals as well as from at least subpopulations of glutamatergic and GABAergic terminals. Both ACh and ATP fulfill the criteria postulated for neurotransmitters. More recent evidence reveals that the two messengers are not confined to neural functions, exerting a considerable variety of non-neural functions in non-innervated tissues. While it has long been known that a substantial number of pathologies originate from malfunctions of the cholinergic system there is now ample evidence that numerous pathological conditions have a purinergic component.