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)

Low level, chronic exposure (0.1 nM, 24 hrs) to the organophosphate paraoxon significantly inhibits N-[3H]methylscopolamine ([3H]NMS) binding to muscarinic receptors in a noncompetitive manner in the SK-N-SH neuroblastoma cell line. The effect of paraoxon on muscarinic receptor-mediated phosphoinositide hydrolysis was also investigated. At 0.1 nM, paraoxon caused a time-dependent increase in the accumulation of inositol phosphates, while the classical muscarinic receptor agonist carbachol was virtually ineffective at low concentrations. In contrast, carbachol-induced increases in phosphoinositide hydrolysis at higher concentrations (1 mM) were markedly larger (five-fold) than the increases induced by PX. Approximately 50% of the maximal increase in the accumulation of inositol phosphates due to paraoxon treatment was antagonized by saturating concentrations of muscarinic receptor antagonists, while the response to carbachol was completely antagonized. In addition, chronic treatment (24 hrs) of SK-N-SH cells with pertussis toxin blocked 75% of the stimulatory effects of carbachol, but inhibited only 38% of the paraoxon-induced response. Neomycin, a phospholipase C inhibitor, completely blocked both the paraoxon and carbachol-induced stimulation of phosphoinositide hydrolysis. The results suggest that paraoxon can modulate signal transduction by indirect activation of muscarinic receptors as well as by acting at a distal site along the pathway.
 ...
PMID:Organophosphate-induced alterations in muscarinic receptor binding and phosphoinositide hydrolysis in the human SK-N-SH cell line. 133 18

The feasibility of using a permeabilized preparation of human SH-SY-5Y neuroblastoma cells for studies of muscarinic acetylcholine receptor (mAChR) sequestration has been evaluated. Exposure of cells permeabilized with digitonin, streptolysin-O, or the alpha-toxin from Staphylococcus aureus to oxotremorine-M (Oxo-M) for 30 min resulted in a 25-30% reduction in the number of cell surface mAChRs, as monitored by the loss of N[3H]methylscopolamine ([3H]NMS) binding sites. The corresponding value for intact cells was 40%. For cells permeabilized with 20 microM digitonin, the Oxo-M-mediated reduction in [3H]NMS binding was time (t1/2 approximately 5 min) and concentration (EC50 approximately 10 microM) dependent and was agonist specific (Oxo-M > bethanechol = arecoline = pilocarpine). In contrast, no reduction in total mAChR number, as monitored by the binding of [3H]quinuclidinyl benzilate, occurred following Oxo-M treatment. The loss of [3H]NMS sites observed in the presence of Oxo-M was unaffected by omission of either ATP or Ca2+, both of which are required for stimulated phosphoinositide hydrolysis, but could be inhibited by the inclusion of guanosine 5'-O-(2-thiodiphosphate). mAChRs sequestered in response to Oxo-M addition were unmasked when the cells were permeabilized in the presence of higher concentrations of digitonin (80 microM).(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Sequestration of muscarinic cholinergic receptors in permeabilized neuroblastoma cells. 815 29

This study was designed to characterize the muscarinic acetylcholine receptor (mAChR) subtype present in rat exorbital lacrimal gland as well as its biochemical coupling. The nonselective muscarinic antagonist [N-methyl-3H]scopolamine ([3H]NMS) binds with high affinity to a homogeneous population of binding sites in both membranes [dissociation constant (Kd) = 82.3 +/- 3.2 pM] and acinar cell (Kd = 170.3 +/- 20 pM) preparations. Muscarinic antagonist inhibition of [3H]NMS binding is homogeneous with the following order of potency: atropine > or = 4-diphenylacetoxy-N-methylpiperidine (4-DAMP) > pirenzepine > 11-([2-(diethylamino)-ethyl]-1-piperidinyl)-acetyl- 5,11-dihydro-6H-pirido[2,3-b]1,4,benzo diazepine-6-one (AFDX 116). Both the affinity of the selective antagonists 4-DAMP, pirenzepine, and AFDX 116 and Northern blot analysis of lacrimal gland mRNAs show a single mAChR population of the M3 subtype. Muscarinic agonist inhibition of [3H]NMS binding displays both high (approximately 20%)- and low-affinity sites (approximately 80%). Both the receptor occupancy and the stimulation by agonists or the inhibition by antagonists of the accumulation of [3H]inositol phosphate were examined under identical conditions with respect to tissue preparations (acinar cells) and buffer (Krebs-Ringer). Results demonstrate 1) the efficient coupling of the M3 mAChR subtype with the phosphatidylinositol (4,5))bisphosphate-specific phospholipase C activity and 2) that the efficacy of a muscarinic agonist is dependent on its structure. Lastly, comparison of the agonists affinity and potency to trigger the [3H]inositol phosphate accumulation suggests that the occupation of the high-affinity agonist binding state of the M3 mAChR was involved in the cellular response.
 ...
PMID:M3 muscarinic acetylcholine receptor coupling to PLC in rat exorbital lacrimal acinar cells. 833 5

A specific and saturable binding site for [3H]N-methyl-scopolamine ([3H]NMS) was observed in plasma membrane of Fischer rat thyroid (FRT) cells with an equilibrium dissociation constant (K(d)) of 0.11 +/- 0.02 nM and a concentration of receptor sites (B(max)) of 14.1 +/- 3.9 fmol/mg protein. Pharmacological characterization of this binding site using pirenzepine, himbacine, (11(2-diethyl-amino)methyl)-1-piperidinylacetyl-5-11-dihydro-6H-pyrido(14) benzodiazepine (AF-DX 116), dicyclomine, 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP), and hexahydro-sila-difenidol (HHSD) showed clear differences, in terms of affinities, between these muscarinic receptor antagonists. The order of potency for inhibiting [3H]NMS binding was HHSD = dicyclomine > 4-DAMP > pirenzepine = himbacine > AF-DX 116. These findings suggest that the muscarinic receptors found in FRT cells belong to the M3 subtype. Stimulation of FRT cells with carbachol produced a biphasic and dose-dependent increase in the intracellular calcium concentration ([Ca2+]i), which was blocked in pretreated cells with atropine and almost abolished by a low concentration of 4-DAMP and HHSD. Removal of extracellular Ca2+ from the incubation medium reduced the initial transient peak and completely abolished the plateau phase, while the transient phase was markedly reduced by the phospholipase C inhibitor U73122. These data indicate that [Ca2+]i results from both Ca2+ influx across Ca2+ channels and mobilization of Ca2+ from intracellular Ca2+ stores. The present data showed the presence of the M3 muscarinic acetylcholine receptor subtype in plasma membrane of FRT cells, which may influence cellular function via modulation of [Ca2+]i.
 ...
PMID:Muscarinic receptor subtypes and calcium signaling in Fischer rat thyroid cells. 1117 38

In recurrent airway obstruction (RAO) or heaves, bronchospasm has been attributed to enhanced cholinergic activity. However, the expression and function of muscarinic acetylcholine receptors (mAChR) and their signaling components are not yet known. Thus, we examined the expression, subtype distribution and postreceptor signaling pathways of mAChR in the peripheral lung, bronchial and tracheal epithelia with the underlying smooth muscle from nine horses with RAO and 11 healthy control horses. In RAO horses, no significant segment-dependent alteration in mAChR density and subtype distribution (assessed by [N-methyl-3H]-scopolamine binding; ([3H]-NMS)), was found, except a trend in receptor down-regulation in some peripheral parts of the lung. The total number of high mAChR binding sites (assessed by carbachol-displacement experiments in the presence or absence of guanosine 5'-triphosphate) was not changed in RAO, suggesting that the functional coupling of mAChR to the corresponding G-proteins is intact. The M2-mediated inhibition of adenylate cyclase (AC) as well as the M3-receptor-G(q/11)-phospholipase C (PLC) activity was not different between RAO and control airway tissues. In conclusion, in equine RAO airways, mAChR expression and function were not altered, and thus appear not to account for the enhanced cholinergic activity in RAO.
 ...
PMID:Equine recurrent airway obstruction does not alter airway muscarinic acetylcholine receptor expression and subtype distribution. 1780 31