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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of lanthanum on the activity of purified preparations of acetylcholinesterase (AChE) from the electric organ of E. electricus and on the activity of AChE in intact electroplaques from the same species were studied. 0.1 mM LaCl3 produced an initial inhibition of purified AChE which was followed by a delayed activation of the enzyme. Upon pretreatment of purified enzyme with LaCl3, initial activity was markedly increased. LaCl3 exerted a marked, concentration-dependent inhibition of intact cell AChE. La3+ and Ca2+ appear to interact competitively. In the presence of both 10 mM CaCl2 and 0.1 mM LaCl3, the initial activitity of purified AChE was increased at lower ACh concentrations and inhibited at ACh concentrations greater than 3 X 10(-4) M. Inhibition of intact cell enzyme by 0.1 mM LaCl3 was relieved by increasing the CaCl2 concentration to 10 mM at ACh concentrations less than 2 X 10(-4) M. The data were analyzed assuming Michaelis-Menten kinetics and interpreted with reference to the differential binding of divalent and trivalent cations to regulatory anionic sites which are separate and distinct from the anionic site of the active center of the enzyme.
Mol Cell Biochem 1977 May 31
PMID:Interactions of lanthanum with purified and intact cell acetylcholinesterase of Electrophorus electricus. 88 82

Neuronal nicotinic acetylcholine receptors (AChRs) are composed of two types of subunits: ACh-binding (termed alpha 2, alpha 3, alpha 4 ...) and structural (termed beta 2, beta 3, beta 4 ...). AChR subtypes composed of combinations of subunits of these two types encoded by several related genes are expressed in different parts of the nervous system, where they presumably serve different functional roles. Here we identify the ACh-binding subunit of the most prominent chicken brain AChR subtype by N-terminal amino acid sequence and show that it corresponds to the alpha 4 gene. Previously we identified the structural subunit for this AChR subtype from chicken brain as beta 2 by N-terminal amino acid sequence. Thus, this identifies both genes which encode subunits of the major nicotinic AChR subtype in avian brains. By immunoprecipitation, immunohistochemistry, and northern blot analysis we show that alpha 3 (or a very closely related sequence) is expressed at low levels in the brain and relatively high levels in the retina, while alpha 4 is expressed at high levels in the brain and lower levels in the retina. This differential expression indicates that alpha 3-containing 'ganglionic-type' AChRs may be an important AChR subtype in avian retina.
Brain Res Mol Brain Res 1991 Apr
PMID:Expression of nicotinic acetylcholine receptor subtypes in brain and retina. 164 84

The role of the conserved N-glycosylation site on each subunit of the Torpedo acetylcholine receptor (AChR) in the biogenesis and function of the receptor was examined by expressing site-directed mutant subunits in Xenopus oocytes. Different mutant subunits caused different effects. The most striking effect was seen with the mutant gamma subunit which, when co-expressed with alpha, beta, and delta subunits, caused degradation of all the subunits. N-Glycosylation of the other subunits appears to contribute to stability of the subunits and/or efficient insertion of the receptor into the plasma membrane, but is not required for assembly. The AChRs containing the mutant alpha subunit formed functional ion channels in the plasma membrane and their activity could be blocked by alpha-bungarotoxin (alpha-BuTX). Thus, attachment of a carbohydrate moiety at the conserved N-glycosylation site is not an absolute requirement for the formation of ACh and alpha-BuTX binding sites.
Brain Res Mol Brain Res 1991 Aug
PMID:Site-directed mutagenesis of the conserved N-glycosylation site on the nicotinic acetylcholine receptor subunits. 166 42

The purpose of the present study was to determine the subtype of muscarinic receptor involved in the action of cholinergic stimuli on synthesis of prostacyclin, measured as immunoreactive 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha), and cGMP in bovine aortic endothelial and rabbit vascular smooth muscle cells. Acetylcholine and arecaidine propargyl ester, a selective M2 agonist, produced a dose-dependent increase in 6-keto-PGF1 alpha output and cGMP formation in confluent endothelial cells but not in confluent vascular smooth muscle cells. McN-A-343, a selective M1 agonist, failed to alter basal 6-keto-PGF1 alpha or cGMP synthesis. Acetylcholine- and arecaidine propargyl ester-induced 6-keto-PGF1 alpha synthesis and cGMP formation in endothelial cells were attenuated by atropine, AF-DX 116 (M2 antagonist), and hexahydrosiladifenidol (M3 antagonist) but not by pirenzepine (M1 antagonist). The cyclooxygenase inhibitor indomethacin abolished 6-keto-PGF1 alpha synthesis but not the increase in cGMP formation elicited by the cholinergic stimuli. Our data suggest that the effect of cholinergic stimuli to enhance prostacyclin and cGMP synthesis is mediated via activation of M2 and M3 receptors located on endothelial cells and that the increase in cGMP production is independent of prostaglandins.
Mol Pharmacol 1991 Jul
PMID:Muscarinic receptor-mediated prostacyclin and cGMP synthesis in cultured vascular cells. 167 48

1. The uptake of [3H] adenosine into specific populations of cells in the inner retina has been demonstrated. In mammalian retina, the exogenous adenosine that is transported into cells is phosphorylated, thereby maintaining a gradient for transport of the purine into the cell. 2. Endogenous stores of adenosine have been demonstrated by localization of cells that are labeled for adenosine-like immunoreactivity. In the rabbit retina, certain of these cells, the displaced cholinergic, GABAergic amacrine cells, are also labeled for adenosine. 3. Purines are tonically released from dark-adapted rabbit retinas and cultured embryonic chick retinal neurons. Release is significantly increased with K+ and neurotransmitters. The evoked release consists of adenosine, ATP, and purine metabolites, and while a portion of this release is Ca2+ dependent, one other component may occur via the bidirectional purine nucleoside transporter. 4. Differential distributions of certain enzymes involved in purine metabolism have also been localized to the inner retina. 5. Heterogeneous distributions of the two subtypes of adenosine receptors, A1 and A2, have been demonstrated in the mammalian retina. Coupling of receptors to adenylate cyclase has also been demonstrated. 6. Adenosine A1 receptor agonists significantly inhibit the K(+)-stimulated release of [3H]-acetylcholine from the rabbit retina, suggesting that endogenous adenosine may modulate the light-evoked or tonic release of ACh.
Cell Mol Neurobiol 1991 Oct
PMID:Adenosine in vertebrate retina: localization, receptor characterization, and function. 168 15

Calcitonin gene-related peptide (CGRP) is present in embryonic chick motoneurons and their terminals during myogenesis. We have studied the effect of CGRP on the expression of mRNA encoding the four subunits (alpha, beta, gamma, delta) of ACh receptors in cultured myotubes derived from embryonic chicks. Northern blot analysis showed that treatment with 10(-7) M CGRP caused an increase in ACh receptor alpha-subunit mRNA expression but did not affect the expression of beta-, gamma-, or delta-subunit mRNAs. In addition, CGRP treatment caused an increase in the expression of unspliced alpha-subunit RNA, suggesting that CGRP increases transcription of the alpha-subunit gene. The effect of CGRP on alpha-subunit gene transcription was mimicked by forskolin, and both CGRP and forskolin increased the levels of intracellular cAMP. We infer that the effect of CGRP on alpha-subunit gene transcription is likely to be mediated by the CGRP-induced rise in intracellular cAMP.
J Mol Neurosci 1991
PMID:Evidence that CGRP and cAMP increase transcription of AChR alpha-subunit gene, but not of other subunit genes. 168 55

ACh receptors (AChRs) synthesized in Xenopus oocytes which were cultured in medium containing gentamicin desensitized much more rapidly than those expressed in the absence of gentamicin. The effect caused by 24 h incubation in gentamicin could not be reversed by leaving oocytes in culture medium without gentamicin for 24 h. In addition, gentamicin exhibited a direct reversible blocking action on the function of AChRs. Our experiments indicate that antibiotics should be used cautiously in culturing oocytes when studying the function of induced neurotransmitter receptors and ion channels.
Brain Res Mol Brain Res 1991 Jan
PMID:Antibiotics cause changes in the desensitization of ACh receptors expressed in Xenopus oocytes. 170 75

Quantitatively, the major phospholipid in the muscle of the nematode Ascaris suum was found to be phosphatidylcholine (lecithin). Stimulation of Ascaris muscle with acetylcholine or the agonists carbachol and levamisole increased the level of phosphorylcholine, 1,2-diacylglycerides and phosphatidic acid. Increased levels of these compounds, together with the demonstration of phospholipase C activity, suggest that phospholipid hydrolysis may be associated with the ACh response of the muscle via second messenger pathways. In other tissues, diacylglycerides and phosphatidic acid have been reported to regulate protein kinase C activity. Protein kinase C activity also was demonstrated in the muscle of Ascaris. For optimal activity the kinase was dependent upon Ca2+, unsaturated 1,2-diacylglyceride and phospholipid. All of the data are in accord with the possible involvement of a second messenger system being operative in the ACh-stimulated contraction of Ascaris muscle.
Mol Biochem Parasitol 1991 Oct
PMID:Phospholipids and protein kinase C in acetylcholine-dependent signal transduction in Ascaris suum. 176 27

Guanine nucleotide binding (G) proteins are heterotrimers that couple a wide range of receptors to ionic channels. The coupling may be indirect, via cytoplasmic agents, or direct, as has been shown for two K+ channels and two Ca2+ channels. One example of direct G protein gating is the atrial muscarinic K+ channel K+[ACh], an inwardly rectifying K+ channel with a slope conductance of 40 pS in symmetrical isotonic K+ solutions and a mean open lifetime of 1.4 ms at potentials between -40 and -100 mV. Another is the clonal GH3 muscarinic or somatostatin K+ channel, also inwardly rectifying but with a slope conductance of 55 pS. A G protein, Gk, purified from human red blood cells (hRBC) activates K+ [ACh] channels at subpicomolar concentrations; its alpha subunit is equipotent. Except for being irreversible, their effects on gating precisely mimic physiological gating produced by muscarinic agonists. The alpha k effects are general and are similar in atria from adult guinea pig, neonatal rat, and chick embryo. The hydrophilic beta gamma from transducin has no effect while hydrophobic beta gamma from brain, hRBCs, or retina has effects at nanomolar concentrations which in our hands cannot be dissociated from detergent effects. An anti-alpha k monoclonal antibody blocks muscarinic activation, supporting the concept that the physiological mediator is the alpha subunit not the beta gamma dimer. The techniques of molecular biology are now being used to specify G protein gating. A "bacterial" alpha i-3 expressed in Escherichia coli using a pT7 expression system mimics the gating produced by hRBC alpha k.
Crit Rev Biochem Mol Biol 1990
PMID:Roles of G proteins in coupling of receptors to ionic channels and other effector systems. 217 76

1. Possible interactions of contrathion (pralidoxime sulfomethylate), a reactivator of phosphorylated acetylcholinesterase (AChE), with the regulation of cholinergic transmission were investigated on an identified synapse in the buccal ganglion of Aplysia californica. 2. Transmitter release was evoked either by a presynaptic action potential or, under voltage clamp, by a long depolarization of the presynaptic cell. At concentrations higher than 10(-5) M, bath-applied contrathion decreased the amplitude of miniature postsynaptic currents and increased their decay time. At the same time, the quantal release of ACh was transiently facilitated. The facilitatory effect of contrathion was prevented by tubocurarine but not by atropine. Because in this preparation, these drugs block, respectively, the presynaptic nicotinic-like and muscarinic-like receptors involved in positive and negative feedback of ACh release, we proposed that contrathion activates presynaptic nicotinic-like receptors. 3. Differential desensitization of the presynaptic receptors is proposed to explain the transience of the facilitatory action of contrathion on ACh release. 4. The complexity of the synaptic action of contrathion raises the possibility that its therapeutic effects in AChE poisonings are not limited to AChE reactivation.
Cell Mol Neurobiol 1990 Sep
PMID:Receptor-mediated presynaptic facilitation of quantal release of acetylcholine induced by pralidoxime in Aplysia. 225 62


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