Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In atrial myocytes, an initial exposure to acetylcholine (ACh1) exerts a short-term conditioning effect such that a second ACh exposure (ACh2) activates ATP-sensitive K+ current (IK,ATP). The purpose of the present study was to determine the mechanism underlying the short-term conditioning induced by ACh that results in subsequent ACh-induced activation of IK.ATP. Cat atrial myocytes were studied using a nystatin-perforated patch whole cell recording method. Changes in L-type Ca2+ current (ICa,L) amplitude were used as an index of relative changes in cyclic AMP (cAMP). The results show that when atrial myocytes are treated with two consecutive exposures to 10 microM ACh separated by a recovery interval, ACh2 activates a larger increase in potassium conductance (gK+) than ACh1. The additional ACh2-induced increase in gK+ is selectively blocked by 10 microM glibenclamide, identifying the current as IK,ATP. Moreover, ICa,L activated immediately after the withdrawal of ACh1 exhibited a transient increase in amplitude above control (+ 76%), consistent with rebound stimulation of cAMP. Rp-cAMPs (50 microM), a selective antagonist of cAMP-dependent protein kinase A, blocked the rebound stimulation of ICa,L and abolished ACh2-induced activation of IK,ATP. Thapsigargin (5 microM), an inhibitor of Ca2+ ATPase in the sarcoplasmic reticulum (SR), abolished ACh2-induced activation of IK,ATP without decreasing rebound stimulation of ICa,L. Rebound stimulation of ICa,L and ACh2-induced activation of IK,ATP both varied as a function of ACh1 duration. We conclude that withdrawal of an initial ACh exposure elicits a rebound cAMP-mediated stimulation of SR Ca2+ uptake. This mechanism induces a short-term conditioning in atrial myocytes such that a subsequent ACh exposure activates IK,ATP. The present results demonstrate novel cholinergic signaling mechanisms in the regulation of IK,ATP.
J Mol Cell Cardiol 1997 Mar
PMID:Cholinergic short-term conditioning and activation of ATP-sensitive K+ current in cat atrial myocytes. 915 51

We describe and functionally characterize six mutations of the acetylcholine receptor (AChR) epsilon subunit gene in three congenital myasthenic syndrome patients. Endplate studies demonstrated severe endplate AChR deficiency, dispersed endplate regions and well preserved junctional folds in all three patients. Electrophysiologic studies were consistent with expression of the fetal gamma-AChR at the endplates in one patient, prolongation of some channel events in another and gamma-AChR expression as well as some shorter than normal channel events in still another. Genetic analysis revealed two recessive and heteroallelic epsilon subunit gene mutations in each patient. One mutation in each (epsilonC190T [epsilon R64X], epsilon 127ins5 and epsilon 553del 7) generates a nonsense codon that predicts truncation of the epsilon subunit in its N-terminal, extracellular domain; and one mutation in each generates a missense codon (epsilon R147L, epsilon P245L and epsilon R311W). None of the mutations was detected in 100 controls. Expression studies in HEK cells indicate that the three nonsense mutations are null mutations and that surface expression of AChRs harboring the missense mutations is significantly reduced. Kinetic analysis of AChRs harboring the missense mutations show that epsilon R147L is kinetically benign, epsilon P245L prolongs burst open duration 2-fold by slowing the rate of channel closing and epsilon R311W shortens burst duration 2-fold by slowing the rate of channel opening and speeding the rate of ACh dissociation. The modest changes in activation kinetics are probably overshadowed by reduced expression of the missense mutations. The consequences of the endplate AChR deficiency are mitigated by persistent expression of gamma-AChR, changes in the release of transmitter quanta and appearance of multiple endplate regions on the muscle fiber.
Hum Mol Genet 1997 May
PMID:Congenital myasthenic syndromes due to heteroallelic nonsense/missense mutations in the acetylcholine receptor epsilon subunit gene: identification and functional characterization of six new mutations. 915 50

Congenital myasthenic syndromes are a group of rare genetic disorders that compromise neuromuscular transmission. A subset of these disorders, the slow-channel congenital myasthenic syndrome (SCCMS), is dominantly inherited and has been shown to involve mutations within the muscle acetylcholine receptor (AChR). We have identified three new SCCMS mutations and a further familial case of the alpha G153S mutation. Single channel recordings from wild-type and mutant human AChR expressed in Xenopus oocytes demonstrate that each mutation prolongs channel activation episodes. The novel mutations alpha V156M, alpha T254I and alpha S269I are in different functional domains of the AChR alpha subunit. Whereas alpha T254I is in the pore-lining region, like five of six previously reported SCCMS mutations, alpha S269I and alpha V156M are in extracellular domains. alpha S269I lies within the short extracellular sequence between M2 and M3, and identifies a new region of muscle AChR involved in ACh binding/channel gating. alpha V156M, although located close to alpha G153S which has been shown to increase ACh binding affinity, appears to alter channel function through a different molecular mechanism. Our results demonstrate heterogeneity in the SCCMS, indicate new regions of the AChR involved in ACh binding/channel gating and highlight the potential role of mutations outside the pore-lining regions in altering channel function in other ion channel disorders.
Hum Mol Genet 1997 May
PMID:Mutations in different functional domains of the human muscle acetylcholine receptor alpha subunit in patients with the slow-channel congenital myasthenic syndrome. 915 51

Autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) is the first, and to date only, idiopathic epilepsy for which a specific mutation has been found. A missense mutation in the critical M2 domain of the alpha4 subunit of the neuronal nicotinic acetylcholine receptor (CHRNA4) has been recently identified in one large Australian pedigree. Here we describe a novel mutation in the M2 domain of the CHRNA4 gene in a Norwegian family. Three nucleotides (GCT) were inserted at nucleotide position 776 into the coding region for the C-terminal end of the M2 domain. Physiological investigations of the receptor reconstituted with the mutated CHRNA4 subunit reveal that this insertion does not prevent the receptor function but increases its apparent affinity for ACh. In addition, this mutant receptor shows a significantly lower calcium permeability that, at the cellular level, may correspond to a loss of function. Comparison of the two mutations identified so far in families with ADNFLE illustrates that different mutations can result in similar phenotypes.
Hum Mol Genet 1997 Jun
PMID:An insertion mutation of the CHRNA4 gene in a family with autosomal dominant nocturnal frontal lobe epilepsy. 917 43

The vasodilator effects of acetylcholine were examined in methoxamine-preconstricted perfused kidneys taken from rats with streptozotocin (STZ)-induced diabetes. Acetylcholine-dependent vasodilatation was significantly weaker in STZ-induced diabetic rats than in age-matched controls, and it was completely abolished by treatment with 60 mM K+ plus NG-nitro-L-arginine (L-NNA) plus methylene blue in the control rats and was significantly but not completely inhibited by these treatment in the diabetic rats. Although acetylcholine-induced vasodilation was not affected by indomethacin in control rats, it was attenuated by indomethacin in the diabetic rats. Arachidonic acid-induced vasoconstriction was slightly but significantly increased in the diabetic rats. Acetylcholine increased significantly the level of 6-keto-prostaglandin F1 alpha in the effluent from perfused kidneys from diabetic rats. These results suggest that the endothelium-dependent vasodilatation induced by acetylcholine in the renal vascular bed of age-matched control rats is due to the release of nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF), whereas the vasodilatation induced by acetylcholine in the STZ-diabetic kidney also involves prostaglandin I2 as well as NO and EDHF.
Res Commun Mol Pathol Pharmacol 1997 Apr
PMID:Endothelial dysfunction in the perfused kidney from the streptozotocin-induced diabetic rat. 917 68

One of the toxic symptoms of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) is reduction in metabolic rate and subsequent growth retardation. Acetylcholine (ACh) serves as an essential growth factor to facilitate amino acid transport and to promote fetal growth. Hydatidiform mole lacks the capacity for synthesis of ACh, and inhibition of ACh synthesis depresses placental amino acid transport. Therefore, we studied the formation of 2,4,5-acetylcoenzyme A (2,4,5-T-CoA) by acetylcoenzyme A synthase (ACoAS) and the formation of 2,4,5-T-ACh by human placental choline acteyltransferase (ChA) from 2,4,5-T-CoA and choline. In these studies, the widely used analog of 2,4,5-T as an herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D), was also included. These studies have the following results (M +/- S.D.; N,6):1) The enzymatic rates of formation of acetyl-CoA, 2,4,5-T-CoA, and 2,4-D-CoA by ACoAS were 32 +/- 4, 23 +/- 3 and 26 +/- 8 nmol/mg protein/5 min., respectively; 2) There were no significant differences in the maximal amounts (nmol/mg protein) of acetyl-CoA (128 +/- 4), 2,4,5-T-CoA (125 +/- 8) and 2,4-D-CoA (96 +/- 6) formed during the reaction period of 50 min.; 3) 14C-2,4-ACh was formed from 14C-2,4-D-CoA and choline by placental-ChA; 4) Low concentrations (EC50 1-2 microM) of synthetic 2,4,5-T-ACh and 2,4-D-ACh decreased the contraction heights of the rat phrenic nerve-hemidiaphragm when the nerve or the muscle was electrically stimulated, and 5) Similar results were obtained with 2,4,6-T-ACh, an analog of 2,4,5-T-ACh. These observations indicate that chlorophenoxyherbicides form false cholinergic messengers in the nerve, muscle and placenta. These false cholinergic messengers can be formed at both muscarinic and nicotinic synaptic sites and also in non-neuronal cells, where ACh plays an important regulatory role as a local hormone, and act as blocking agents. These results will partially explain myotonia, ventricular fibrillation and fetal growth retardation induced by these herbicides.
Cell Mol Biol (Noisy-le-grand) 1997 Jun
PMID:Cellular toxicity of 2,4,5-trichlorophenoxyacetic acid: formation of 2,4,5-trichlorophenoxyacetylcholine. 922 Jan 48

We examined the possible existence of a novel endothelium-derived relaxing factor in the endothelium of the perfused rat kidney. Acetylcholine-induced vasodilatation was abolished by treatment with NG-nitro-L-arginine (L-NNA) and methylene blue in isotonic high K+ (60 mM) medium, whereas cyclopiazonic acid (CPA)-induced vasodilatation of the perfused kidney was slightly increased by this treatment. When the kidney was perfused with 0.47% CHAPS solution for 1 min, acetylcholine- or cyclopiazonic acid-induced vasodilatation was almost abolished. Acetylcholine- or cyclopiazonic acid-induced vasodilatation was not affected by indomethacin. These results suggest that CPA may release a novel endothelium-derived relaxing factor, which is not prostanoids, nitric oxide nor endothelium-derived hyperpolarizing factor in the endothelium of the renal vascular bed.
Res Commun Mol Pathol Pharmacol 1997 May
PMID:Characteristics of vasodilatation induced by cyclopiazonic acid in the rat perfused kidney. 922 49

We studied the mechanism of action of methylene blue (Mblue), a putative guanylyl cyclase inhibitor, on the L-type calcium current (ICa) and the muscarinic activated K+ current (IK,ACh) in rat ventricular and atrial myocytes, respectively, and on the binding of [3H]quinuclidinyl benzylate in rat ventricular membranes. Superfusion, but not internal dialysis, with 30 microM Mblue antagonized the inhibitory effect of acetylcholine (ACh, 1 microM) on beta-adrenergic stimulation of ICa with isoprenaline (Iso, 10 nM or 1 microM). However, Mblue had no effect on the basal ICa or on the stimulation of ICa by Iso in the absence of ACh. The activation of IK,ACh by 3 microM ACh was also antagonized by Mblue in a dose-dependent manner. In contrast, Mblue had no effect on the activation of IK,ACh by either guanosine-5'-O-(3-thio)triphosphate or guanosine-5'-(beta,gamma-imido)triphosphate. Chlorpromazine (CPZ), a piperazine derivative like Mblue, also inhibited the muscarinic activation of IK,ACh in a dose-dependent manner. The specific binding of [3H]QNB, a muscarinic ligand, to rat ventricular membranes was displaced in a dose-dependent manner by Mblue and CPZ. The piperazine derivatives behaved like competitive antagonists of [3H]QNB binding, exhibiting equilibrium dissociation constant (Ki) values of 187 nM for Mblue and 366 nM for CPZ. In conclusion, Mblue exerts antimuscarinic effects on ICa and IK,ACh in rat cardiac myocytes that are best explained by the binding of Mblue to the M2 subtype of muscarinic receptors. This property probably contributes to the antimuscarinic effect of the putative guanylyl cyclase inhibitor reported in previous studies.
Mol Pharmacol 1997 Sep
PMID:Methylene blue is a muscarinic antagonist in cardiac myocytes. 928 11

Acetylcholine stimulation of bovine chromaffin cells results in increased norepinephrine and epinephrine secretion accompanied by a corresponding increase in synthesis. The addition of neuropeptide Y (NPY) to the culture medium prevents the increase in catecholamine synthesis but not secretion. Treatment of chromaffin cells with nicotine produces a concentration-dependent increase in tyrosine hydroxylase activity (IC50 = 1.2 microM) that is reduced if NPY is present during stimulation. Tyrosine hydroxylase activity decreases in a concentration-dependent fashion if increasing amounts of NPY are included in the culture medium, IC50 = 0.2 nM. Treatment with pertussis toxin completely prevents the effect of NPY. The rank order of potency for inhibition of tyrosine hydroxylase activity is NPY > or = [Leu31,Pro34]NPY > or = peptide YY > NPY2-36 > NPY13-36 > NPY18-36 > or = NPY26-36 >> NPY1-30, suggesting a NPY-Y1 receptor subtype. Examination of the effect of NPY on nicotine stimulation of chromaffin cell protein phosphorylation showed that NPY produces a concentration-dependent decrease in a 60-kDa protein, IC50 = 6.4 nM. The effect of NPY is pertussis toxin-sensitive. The rank order of potency is [Leu31,Pro34]NPY > or = NPY >> NPY18-36. Immunoprecipitation confirmed the identity of the 60-kDa protein as tyrosine hydroxylase.
Mol Pharmacol 1997 Dec
PMID:Neuropeptide Y inhibits chromaffin cell nicotinic receptor-stimulated tyrosine hydroxylase activity through a receptor-linked G protein-mediated process. 941 12

We studied the interactions of strychnine, brucine, and three of the N-substituted analogues of brucine with [3H]N-methylscopolamine (NMS) and unlabeled acetylcholine at m1-m5 muscarinic receptors using equilibrium and nonequilibrium radioligand binding studies. The results were consistent with a ternary allosteric model in which both the primary and allosteric ligands bind simultaneously to the receptor and modify the affinities of each other. The compounds had Kd values in the submillimolar range, inhibited [3H]NMS dissociation, and showed various patterns of positive, neutral, and negative cooperativity with [3H]NMS and acetylcholine, but there was no predictive relationship between the effects. Acetylcholine affinity was increased approximately 2-fold by brucine at m1 receptors, approximately 3-fold by N-chloromethyl brucine at m3 receptors, and approximately 1.5-fold by brucine-N-oxide at m4 receptors. The existence of neutral cooperativity, in which the compound bound to the receptor but did not modify the affinity of acetylcholine, provides the opportunity for a novel form of drug selectivity that we refer to as absolute subtype selectivity: an agent showing positive or negative cooperativity with the endogenous ligand at one receptor subtype and neutral cooperativity at the other subtypes would exert functional effects at only the one subtype, regardless of the concentration of agent or its affinities for the subtypes. Our results demonstrate the potential for developing allosteric enhancers of acetylcholine affinity at individual subtypes of muscarinic receptor and suggest that minor modification of a compound showing positive, neutral, or low negative cooperativity with acetylcholine may yield compounds with various patterns of cooperativity across the receptor subtypes.
Mol Pharmacol 1998 Mar
PMID:Subtype-selective positive cooperative interactions between brucine analogues and acetylcholine at muscarinic receptors: radioligand binding studies. 949 26


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