Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.4.3 (phospholipase C)
 18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. Acetylcholine (ACh) produces two membrane current changes when applied to NG108-15 mouse neuroblastoma x rat glioma hybrid cells transformed (by DNA transfection) to express m1 muscarinic receptors: it activates a Ca(2+)-dependent K+ conductance, producing an outward current, and it inhibits a voltage-dependent K+ conductance (the M conductance), thus diminishing the M-type voltage-dependent K+ current (IK(M)) and producing an inward current. The present experiments were undertaken to find out how far inhibition of IK(M) might be secondary to stimulation of phospholipase C, by recording membrane currents and intracellular Ca2+ changes with indo-1 using whole-cell patch-clamp methods. 2. Bath application of 100 microM ACh reversibly inhibited IK(M) by 47.3 +/- 3.2% (n = 23). Following pressure-application of 1 mM ACh, the mean latency to inhibition was 420 ms at 35 degrees C and 1.79 s at 23 degrees C. Latencies to inhibition by Ba2+ ions were 148 ms at 35 degrees C and 92 ms at 23 degrees C. 3. The involvement of a G-protein was tested by adding 0.5 mM GTP-gamma-S or 10 mM potassium fluoride to the pipette solution. These slowly reduced IK(M), with half-times of about 30 and 20 min respectively, and rendered the effect of superimposed ACh irreversible. Effects of ACh were not significantly changed after pretreatment for 24 h with 500 ng ml-1 pertussis toxin or on adding up to 10 mM GDP-beta-S to the pipette solution. 4. The role of phospholipase C and its products was tested using neomycin (to inhibit phospholipase C), inositol 1,4,5-trisphosphate (InsP3) and inositol 1,3,4,5-tetrakisphosphate (InsP4), heparin, and phorbol dibutyrate (PDBu) and staurosporin (to activate and inhibit protein kinase C respectively). Both neomycin (1 mM external) and InsP3 (100 microM intrapipette) inhibited the ACh-induced outward current and/or intracellular Ca2+ transient but did not block ACh-induced inhibition of IK(M). Intrapipette heparin (1 mM) blocked activation of IK(Ca) and reduced Ach-induced inhibitions of IK(M), but also reduced inhibition of ICa via endogeneous m4 receptors. PDBu (with or without intrapipette ATP) and staurosporin had no significant effects.(ABSTRACT TRUNCATED AT 400 WORDS)
 ...
PMID:On the mechanism of M-current inhibition by muscarinic m1 receptors in DNA-transfected rodent neuroblastoma x glioma cells. 827 Nov 96

The effects of 5 mM NaF + 10 microM AlCl3, a direct activator of guanine nucleotide-binding proteins (G proteins), on the release of [3H]dopamine ([3H]DA), [3H]gamma-aminobutyric acid ([3H]GABA), and [3H]acethylcholine ([3H]ACh) were investigated in slices of rat striatum. When the tissue was exposed to NaF + AlCl3 the release of [3H]DA, [3H]GABA, and [3H]ACh was enhanced significantly. In a calcium-free solution the release of [3H]GABA and [3H]DA was increased by NaF+AlCl3 much more than in the presence of [Ca2+]o. In slice preparations taken from reserpinized animals, in which the vesicular storage of [3H]DA was therefore prevented, NaF + AlCl3 had no effect on [3H]DA release. HPLC analysis of the radioactivity of the perfusate showed that, in the presence of NaF + AlCl3, the content of dihydroxyphenylacetic acid (DOPAC) in perfusate samples increased significantly, while in pargyline-treated animals only the DA content was increased. Inhibition of DA carriers by nomifensine or low temperature prevented the effect of NaF + AlCl3. N-ethylmaleimide (NEM) preincubation did not modify the effect of NaF + AlCl3 on [3H]DA release Neomycin (0.1 mM), a phospholipase C (PLC) inhibitor, significantly decreased the effect of NaF + AlCl3 on [3H]DA and [3H]GABA release. The internal concentration of Ca2+ in synaptosomes was enhanced by NaF + AlCl3 in normal solution. However, [Ca2+]i was not influenced by NaF + AlCl3 in Ca(2+)-free medium. It is concluded that a non-receptor-mediated activation, by NaF + AlCl3, of the alpha-subunit of a G protein, results in a [Ca2+]o-independent release of DA and GABA, but not that of ACh.
 ...
PMID:Transmitter release by non-receptor activation of the alpha-subunit of guanine nucleotide regulatory protein in rat striatal slices. 856 25

Outer (OHC) and inner (IHC) hair cells in the organ of Corti of the mammalian cochlea process sound. OHC and their efferent synapse are part of a feedback system assumed to control and modulate information carried by afferent neurons passing from IHC to the brain. Underlying mechanisms are not well understood. This paper discusses recent progress. In vivo and in vitro information is presented on structure, pharmacology, function and localization of the pre- and postsynaptic acetylcholine receptors (AChRs) at the efferent synapse. Recent data are given on a presynaptic M3 AChR subtype, probably an autoreceptor involved in transmitter release. Data from our lab on specific binding of [3H]3-quinuclidinyl benzilate ([3H]3-QNB) to non-enzymatically isolated guinea pig OHC reveal a KD several 100 x higher than that for any known muscarinic receptor subtype, including the above-mentioned presynaptic muscarinic AChR of the OHC efferent synapse. The extremely high concentrations of [3H]3-QNB needed for any binding at all to OHC thus rule out presynaptic membrane impurities as the cause of such binding, and also the presence of a typical mAChR subtype on OHC. The number of [3H]3-QNB binding sites (approximately 10(6)/OHC) we found on OHC was 1/10th of that we found for binding of nicotinic ligands to OHC, further making it questionable that an ACh-binding site on OHC binds [3H]3-QNB. Observations may instead point to the possibility of another binding site, e.g. an (allosteric) site involved with the as yet not understood 'weak' muscarinic properties of the OHC AChR. Further new data on the OHC AChR confirm reversible alpha-bungarotoxin, nicotine and d-tubocurarine binding. [3H]alpha-Bungarotoxin and [3H]-nicotine binding sites are estimated at approximately 6.10(7) sites/OHC. Strychnine, a glycine receptor blocker suggested to interfere with cholinergic sites of the efferent OHC synapse, was found to bind to OHC (cold strychnine for unspecific binding). This binding, not seen in the presence of high [glycine], increased in the presence of depolarizing [K+], while ACh (100 microM) had no significant effect. Results suggest strychnine binding to the outside of OHC, but also sites accessible only after cell depolarization, possibly to the hyperpolarizing Ca2(+)-dependent K+ channel. Recent molecular cloning of the OHC AChR indicates a novel alpha-subunit. An often observed ACh-activated Ca(2+)-influx close to zero into OHC leaves an unanswered question. OHC also carry P2-purinergic receptors (P2Rs), a more rapid ionotropic P2zR-like subtype and a quantitatively dominating slow metabotropic P2yR subtype coupled to a G protein-phospholipase C cascade and not desensitized. Both contribute to increased cytoplasmic [Ca2+], from respectively external and internal sources. Whether or not such receptors are part of efferent synaptic activity is unknown; their localization on the OHC plasma membrane is so far only indirect and synaptic vesicles of the efferent nerve endings have not yet been analyzed for their ATP content. Localization, function and interaction of [Ca2+] increases triggered by, respectively, ATP and ACh are currently studied in this laboratory.
 ...
PMID:Cholinergic and purinergic signalling in outer hair cells of mammalian cochlea. 884 30

Lithium has a biphasic effect of the agonist-dependent accumulation of Ins(1,4,5)P3 in human neuroblastoma SH-SY5Y cells. These effects consist of a transient reduction, followed by a long-lasting increase in Ins(1,4,5)P3 as compared to controls. The Li+ effects are dose dependent, and were observed at concentrations used in the treatment of bipolar disorders, and thus may have therapeutic implications. The mechanism of the Li+ effect on Ins(1,4,5)P3 accumulation requires further investigation. The transient reduction of Ins(1,4,5)P3 was observed under conditions where Li+ causes only a moderate increase in the inositol mono- and bi-phosphates. Supplementation with exogenous inositol had no effect on the level of Ins(1,4,5)P3, indicating that the mechanism of the Li(+)-dependent reduction of Ins(1,4,5)P3 is not due to inositol depletion. Li+ did not interfere with degradation of Ins(1,4,5)P3 after receptor-blockage with atropine, suggesting that Li+ has no direct effect on the Ins(1,4,5)P3 metabolizing enzymes. A direct effect of Li+ on the phospholipase C is also unlikely. Entry of Ca2+ into the cells is an important factor, which affects agonist-stimulated accumulation of Ins(1,4,5)P3, as well as absolute values of Li(+)-dependent increase in Ins(1,4,5)P3; however, it is not essential for the manifestation of Li+ effects. Our results also show that manifestation of Li+ effects in human neuroblastoma cells requires the stimulation of muscarinic receptors and activation of PLCs, PKCs, and/or that other staurosporine/H-7/GF 109203X-sensitive protein kinases are involved in the regulation of Ins(1,4,5)P3 during the plateau phase of ACh-stimulation. We also suggest an important role for these enzymes in the Li(+)-dependent elevation of Ins(1,4,5)P3.
 ...
PMID:Phosphoinositide signalling in human neuroblastoma cells: biphasic effect of Li+ on the level of the inositolphosphate second messengers. 886 50

Acetylcholine and adenosine triphosphate (ATP) raise intracellular Ca2+ concentration via muscarinic receptors and P2U purinoceptors by releasing Ca2+ from intracellular Ca2+ stores in the neural retina of early embryonic chick. The signal transduction mechanisms for the muscarinic and purinergic Ca2+ responses were studied with fura-2 fluorescence measurements. Li+ (1 mM), which inhibits phosphatidylinositol metabolism, enhanced both the Ca2+ rises to carbamylcholine (CCh. 30 microM) a muscarinic agonist and ATP (200 microM). Thapsigargin (250 nM), an inhibitor of Ca(2+)-ATPase of inositol trisphosphate (IP3)-sensitive Ca2+ stores, abolished both the Ca2+ rises to CCh (100 microM) and ATP (500 microM). U-73122 (2 microM), an inhibitor of phospholipase C beta, suppressed the Ca2+ rise to ATP (500 microM), but its analog U-73343 (2 microM) did not suppress it. In contrast, both U-73122 and U-73343 suppressed the Ca2+ the Ca2+ rise to CCh (100 microM). Pertussis toxin (250 ng/ml) suppressed the ATP-induced Ca2+ rise at least partly, whereas no inhibition was observed on the CCh-induced Ca2+ rise. Cross-talk occurred between the muscarinic and purinergic Ca2+ mobilizations but they were not occlusive. This study suggests that the muscarinic and purinergic Ca2+ mobilizations utilize IP3-sensitive Ca2+, stores, but different signal transduction pathways are involved in between the muscarinic and purinergic Ca2+ responses.
 ...
PMID:Muscarinic and purinergic Ca2+ mobilizations in the neural retina of early embryonic chick. 896 Sep 76

At the neuromuscular junction and possibly also at the synaptic level in the brain, the main sequence of events (see Fig. 5) that involves purines in modulation of ACh release includes the following observations: (1) storage of ATP and its release either together with, or independently of acetylcholine. ATP is also released from the post-junctional component. Adenosine as such is released either from the motor nerve terminals or from the post-junctional component. (2) There is extracellular hydrolysis of ATP to adenosine, which is the active substance to modulate transmitter release. The key enzyme in the conversion of AMP into adenosine is the ecto 5'-nucleotidase. When ecto-5'-nucleotidase is not available (e.g. in cholinergic nerve terminals of the cerebral cortex) ATP as such exerts the neuromodulatory role normally fulfilled by adenosine. (3) Both the inhibition and the excitation induced by adenosine on ACh release in the rat is inactivated through up-take and deamination. (4) Adenosine-induced inhibition of ACh release is mediated via A1 receptors and the excitation via A2a receptors. The A2a receptors are positively coupled to the adenylate cyclase/cyclic AMP system, whereas the presynaptic A1 receptors (a) may be negatively linked to adenylate cyclase and (b) to phospholipase C, and, upon stimulation, (c) increase potassium conductance and (d) decrease calcium conductance. (5) Activation of A2a receptors is essential for substances that facilitate ACh release (e.g. CGRP, forskolin) to exert their effects, as well as for induction of nicotinic autofacilitatory receptor desensitization. (6) There are interactions between A1 and A2a receptors. Thus, the net adenosine neuromodulatory response is the resultant, at each moment, of the relative degree of activation of each one of these receptors. This relative activation depends upon the intensity (frequency, pulse duration) of stimulation of the motor nerve terminals. (7) Adenosine released as such seems to preferentially activate A1 receptors, whereas the adenosine formed from metabolism of adenine nucleotides prefers to activate the A2a receptors. In conclusion, to find out precisely what occurs with ACh in transmitting its message at the synaptic level, one has to consider the subtle ways used by purines to modulate the ACh response. It therefore appears of interest that pharmacological and therapeutic strategies use this knowledge to approach cholinergic transmission deficiencies based upon reduction of ACh release.
 ...
PMID:Purinergic regulation of acetylcholine release. 900 12

The effect of lithium on the phosphoinositide-signaling pathway was examined in 5-HT2C receptors, which are involved in phospholipase C stimulation, expressed in Xenopus laevis oocytes by voltage-clamp recording and assay of intracellular Ca2+ concentrations. Treatment with lithium for 60 sec after the initial application of 5-HT reduced Ca2+-dependent chloride currents in a dose-dependent manner (0.01-1 mM) and inhibited intracellular Ca2+ release, whereas pretreatment with lithium or injection into oocytes had no effect. Additionally, treatment with lithium for more than 24 hr reduced 5-HT-evoked currents to a much lesser extent. In contrast, the currents through other phosphoinositide-dependent receptors, such as endogenous "serum" and muscarinic ACh receptors, were not affected or less affected by a short term or long term treatment with lithium, respectively. These results indicate that lithium may have a specific blocking effect on the 5-HT2C receptors and, in part, nonselectively act on the phosphoinositide metabolic pathway.
 ...
PMID:A specific inhibitory action of lithium on the 5-HT2c receptor expressed in Xenopus laevis oocytes. 905 2

1. Cytosolic Ca2+ concentration ([Ca2+]i) during exposure to acetylcholine or caffeine was measured in mouse duodenal myocytes loaded with fura-2. Acetylcholine evoked a transient increase in [Ca2+]i followed by a sustained rise which was rapidly terminated after drug removal. Although L-type Ca2+ currents participated in the global Ca2+ response induced by acetylcholine, the initial peak in [Ca2+]i was mainly due to release of Ca2+ from intracellular stores. 2. Atropine, 4-diphenylacetoxy-N-methylpiperidine (4-DAMP, a muscarinic M3 antagonist), pirenzepine (a muscarinic M1 antagonist), methoctramine and gallamine (muscarinic M2 antagonists) inhibited the acetylcholine-induced Ca2+ release, with a high affinity for 4-DAMP and atropine and a low affinity for the other antagonists. Selective protection of muscarinic M2 receptors with methoctramine during 4-DAMP mustard alkylation of muscarinic M3 receptors provided no evidence for muscarinic M2 receptor-activated [Ca2+]i increase. 3. Acetylcholine-induced Ca2+ release was blocked by intracellular dialysis with a patch pipette containing either heparin or an anti-phosphatidylinositol antibody and by external application of U73122 (a phospholipase C inhibitor). 4. Acetylcholine-induced Ca2+ release was insensitive to external pretreatment with pertussis toxin, but concentration-dependently inhibited by intracellular dialysis with a patch pipette solution containing an anti-alpha q/alpha 11 antibody. An antisense oligonucleotide approach revealed that only the Gq protein was involved in acetylcholine-induced Ca2+ release. 5. Intracellular applications of either an anti-beta com antibody or a peptide corresponding to the G beta gamma binding domain of the beta-adrenoceptor kinase 1 had no effect on acetylcholine-induced Ca2+ release. 6. Our results show that, in mouse duodenal myocytes, acetylcholine-induced release of Ca2+ from intracellular stores is mediated through activation of muscarinic M3 receptors which couple with a Gq protein to activate a phosphatidylinositol-specific phospholipase C.
 ...
PMID:Specific Gq protein involvement in muscarinic M3 receptor-induced phosphatidylinositol hydrolysis and Ca2+ release in mouse duodenal myocytes. 917 86

Changes in elemental content in response to muscarinic drugs in HT29 cells were investigated by X-ray microanalysis. Acetylcholine (ACh) and carbachol (Cch), both agonists binding to muscarinic receptors, induced a decrease of the intracellular Cl and K content. This agrees with the notion that these agonists induce electrolyte and water secretion. Atropine, a non-selective antagonist of muscarinic receptors, inhibited the decrease in K and Cl caused by ACh and Cch, and instead caused an increase of the Cl and K concentrations. A similar inhibition was found in the case of the selective muscarinic 3 receptor antagonist P-F-HHSiD. In contrast, the selective muscarinic 2 receptor antagonist AF-DX 116 did not inhibit Cch-activated secretion of K and Cl. A slight inhibition of ACh induced ion secretion was seen, but this inhibition was weak compared to that caused by P-F-HHSiD. Treatment with U-73122, an inhibitor of phospholipase C, blocked ACh or Cch induced ion secretion. These results suggest that ACh and Cch stimulated secretion of Cl and K is mediated by muscarinic 3 receptors via the inositol-1,4,5-trisphosphate (IP3) dependent pathway.
 ...
PMID:Evidence for muscarinic 3 receptor mediated ion transport in HT29 cells studied by X-ray microanalysis. 924 1

Muscarinic m2 and m4 receptors couple preferentially to inhibition of adenylyl cyclase, whereas m1, m3, and m5 receptors couple preferentially to activation of phospholipase C-beta and in some cells to stimulation of cAMP. Smooth muscle cells were shown to express adenylyl cyclases types V and/or VI. Acetylcholine (ACh) stimulated the binding of [35S]GTPgammaS.Galpha complexes in smooth muscle membranes to Galphaq/11 and Galphai3 antibody. Binding to Galphaq/11 antibody was inhibited by the m3 receptor antagonist, 4-DAMP, and binding to Galphai3 antibody was inhibited by the m2 receptor antagonist, N,N'-bis[6[[(2-methoxyphenyl)methyl]amino]hexyl]-1,8-octanediamine tetrahydrochloride (methoctramine). The decrease in basal cAMP (35 +/- 5%) induced by ACh in dispersed muscle cells was accentuated by 4-DAMP or Gbeta antibody (55 +/- 8 to 63 +/- 6%). In contrast, methoctramine, pertussis toxin (PTx), or Galphai3 antibody converted the decrease in cAMP to increase above basal level (+28 +/- 5 to +32 +/- 6%); the increase in cAMP was abolished by 4-DAMP or Gbeta antibody. In muscle cells where only m3 receptors were preserved by selective receptor protection, ACh caused only an increase in cAMP that was abolished by 4-DAMP. Conversely, in muscle cells where only m2 receptors were preserved, ACh caused an accentuated decrease in cAMP that was abolished by methoctramine or PTx. In conclusion, m2 receptors in smooth muscle couple to inhibition of adenylyl cyclases V/VI via Galphai3, and m3 receptors couple to activation of the enzymes via Gbetagammaq/11.
 ...
PMID:Differential coupling of muscarinic m2 and m3 receptors to adenylyl cyclases V/VI in smooth muscle. Concurrent M2-mediated inhibition via Galphai3 and m3-mediated stimulation via Gbetagammaq. 926 Nov 44


<< Previous 1 2 3 4 5 6 7 8 9 Next >>