Acetylcholine, determination

E. (1998) Design and development of an amperometric biosensor for acetylcholine determination in brain microdialysates. Electrochimica Acta, 43 (23), 3541-3554. 

Elucidation of the stmctural requirements for dmg interaction at the recognition site is by the study of stmcture—activity relationships (SAR), in which, according to a specific biologic response, the effects of systematic molecular modification of a parent dmg stmcture are determined. Such studies have permitted the classification of discrete classes of pharmacological receptors. For example, the neurotransmitter acetylcholine acts at both peripheral and central receptors which are of at least three distinct types. The effects of acetylcholine are mimicked in smooth and cardiac muscles and secretory... 

Figure 5. The effects of 0.11 mM acetylcholine on the concentration-dependent inhibition of AChE by ANTX-A(S). Acetylcholine was coincubated with ANTX-A(S) and AChE two minutes before the inhibition rate was determin. Key (o) 0.158 ig/mL (A) 0.079 g/mL ( ) 0.032 Axg/mL (V) 0.016 ng/mU >) 0.0032 ixg/mL ( ). 0016 fig/mL. NOTE Total inhibition occurs when 0.158 fig/mh ANTX-A(S) is preincubated with AChE for two minutes.

Anatoxin-a is the most potent and most stereospecific nicotinic acetylcholine receptor agonist thus far identified. It is also highly selective for nicotinic receptors over muscarinic receptors. The molecular parameters which influence the binding affinity, channel activation, channel blockade, and receptor desensitization are being studied. Modifications of the carbonyl and amine moieties can reduce or nearly eliminate the receptor agonist potency of the compounds and also determine the channel blocking characteristics. 

Organophosphate Ester Hydraulic Fluids. The biomarkers of effects after exposure to organophosphate ester hydraulic fluids are well established in cases of delayed neuropathy (clinical signs of peripheral neuropathy). Further study would be helpful to determine whether certain effects (such as diarrhea after oral exposure) are due to direct action of the toxic agent on the target organ or to inhibition of acetylcholinesterase at the acetylcholine nerve receptor site on the organ. 

Among cations, potassium, acetylcholine, some cationic surfactants (where the ion-exchanger ion is the / -chlorotetraphenylborate or tetra-phenylborate), calcium (long-chain alkyl esters of phosphoric acid as ion-exchanger ions), among anions, nitrate, perchlorate and tetrafluoro-borate (long-chain tetraalkylammonium cations in the membrane), etc., are determined with this type of ion-selective electrodes. 

Acetylcholine is formed from acetyl CoA (produced as a byproduct of the citric acid and glycolytic pathways) and choline (component of membrane lipids) by the enzyme choline acetyltransferase (ChAT). Following release it is degraded in the extracellular space by the enzyme acetylcholinesterase (AChE) to acetate and choline. The formation of acetylcholine is limited by the intracellular concentration of choline, which is determined by the (re)uptake of choline into the nerve ending (Taylor Brown, 1994). 

Isotonic muscle contraction was used to measure the effects of selected nematode FaRPs on the body-wall muscle of H. contortus. AF2 was found to have inhibitory effects on muscle activity and inhibited acetylcholine (ACh) -induced contractions in the worm whereas AF8 had excitatory effects on the muscle and enhanced ACh-induced contractions (Marks et al., 1999a). There were obvious differences in the methodologies used to evaluate the effects of these peptides on Haemonchus muscle compared with those used to examine these peptide effects on Ascaris. How comparable the results are has yet to be determined. 

Fluorine has been used to modulate the basicity of amines which may lead to an improvement in brain exposure. Recently, the discovery of a series of a4(32 nicotinic acetylcholine receptor (nAChR) potentiators as possible treatment for Parkinson s disease and schizophrenia was were disclosed [40]. Optimization of isoxazole 40 included the bioisosteric replacement of the central amide by an imidazole ring. Introduction of a fluorine at the 6-position of the phenyl ring provided compound 41. This compound had excellent potency but was determined to be a substrate for P-gp (efflux ratio >10). In an attempt to reduce amine basicity and decrease the efflux propensity, the 4-fluoropiperidine 42 was identified which retained potency and had significantly reduced P-gp efflux liability (efflux ratio 1). CNS penetration of 42 was observed in rodents following intraperitoneal (IP) treatment at 5mg/kg and showed a brain concentration of 6.5 gM. 

LaRochelle, W.J., and Froehner, S.C. (1986a) Determination of the tissue distributions and relative concentrations of the postsynaptic 43-kDa protein and the acetylcholine receptor in Torpedo. J. Biol. Chem. 261, 5270-5274. 

M. Bernabai, C. Cremisini, M. Mascini, and G. Palleschi, Determination of organophosphorus and car-bamic pesticides with a choline and acetylcholine electrochemical biosensor. Anal. Lett. 24, 1317-1331 (1991). 

A particular interest for clinical applications was a possibility for detection of dopamine by its oxidation on nickel [19], cobalt [65], and osmium [66] hexacyanofer-ates. Except for oxidation of dopamine, cobalt and osmium hexacyanoferrates were active in oxidation of epinephrine and norepinephrine. For clinical analysis it is also important to carry out the detection of morphine on cobalt [67] and ferric [68] hexacyanoferrates, as well as the detection of oxidizable amino acids (cystein, methionine) by manganous [69] and ruthenium [70] hexacyanoferrate-modified electrodes. In general, oxidation of thiols was first shown for Prussian blue [71] and nickel hexacyanoferrate [72], This approach has been used for the detection of thiols in rat striatum microdialysate [73], Alternatively, the detection of thiocholine with Prussian blue was employed for pesticide determination in acetylcholine-esterase test [74],... 

H.C. Tsai and R.A. Doong, Simultaneous determination of pH, urea, acetylcholine and heavy metals using array-based enzymatic optical biosensor. Biosens. Bioelectron. 20, 1796-1804 (2005). 

Tor [7] developed a new method for the preparation of thin, uniform, self-mounted enzyme membrane, directly coating the surface of glass pH electrodes. The enzyme was dissolved in a solution containing synthetic prepolymers. The electrode was dipped in the solution, dried, and drained carefully. The backbone polymer was then cross-linked under controlled conditions to generate a thin enzyme membrane. The method was demonstrated and characterized by the determination of acetylcholine by an acetylcholine esterase electrode, urea by a urease electrode, and penicillin G by a penicillinase electrode. Linear response in a wide range of substrate concentrations and high storage and operational stability were recorded for all the enzymes tested. 

The same group reported in 1986 a sensitive and selective HPLC method employing CL detection utilizing immobilized enzymes for simultaneous determination of acetylcholine and choline [187], Both compounds were separated on a reversed-phase column, passed through an immobilized enzyme column (acetylcholine esterase and choline oxidase), and converted to hydrogen peroxide, which was subsequently detected by the PO-CL reaction. In this period, other advances in this area were carried out such as the combination of solid-state PO CL detection and postcolumn chemical reaction systems in LC [188] or the development of a new low-dispersion system for narrow-bore LC [189],... 

On the other hand, several oxidases are known to generate hydrogen peroxide, acting as an oxidant in the CL system, from corresponding substrates. IMERs in which the oxidases are immobilized on adequate supporting materials such as glass beads have been developed. IMERs are often used for flow injection with CL detection of uric acid and glucose, and are also applicable to the CL determination of acetylcholine, choline, polyamines, enzyme substrates, etc., after online HPLC separation. 

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