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

Pituitary folliculostellate cells (FSCs) are thought to partially inhibit pituitary hormone secretion through a paracrine mechanism. In this process, one of the important questions is what factors regulate the function of FSCs. Because ACh is synthesized in and possibly released from the corticotrophs and lactotrophs, we examined whether FSCs respond to ACh by the method of Ca2+ imaging in primary cultured FSCs from male Wistar rats. ACh (30 nM-3 microM) increased intracellular calcium concentration ([Ca2+](i)) of FSCs in a concentration-dependent manner, with an initial rapid rise followed by a relatively sustained increase. The complete block of the response by atropine and pirenzepine suggests involvement of muscarinic receptors. Depletion of the stored Ca2+ by thapsigargin blocked the response completely. Blockers of phospholipase C, U-73122 and neomycin, suppressed significantly the rise of [Ca2+](i). These results suggest that ACh increases [Ca2+](i) in FSCs by activating phospholipase C, presumably through activation of M(1) receptors. The rise in [Ca2+](i) could trigger a variety of Ca2+-dependent cellular processes, including the synthesis and release of bioactive substances, which in turn act on endocrine cells.
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PMID:Acetylcholine increases intracellular Ca2+ in the rat pituitary folliculostellate cells in primary culture. 1125 68

ATP, besides an intracellular energy source, is an agonist when applied to a variety of different cells including cardiomyocytes. Sources of ATP in the extracellular milieu are multiple. Extracellular ATP is rapidly degraded by ectonucleotidases. Today ionotropic P2X(1--7) receptors and metabotropic P2Y(1,2,4,6,11) receptors have been cloned and their mRNA found in cardiomyocytes. On a single cardiomyocyte, micromolar ATP induces nonspecific cationic and Cl(-) currents that depolarize the cells. ATP both increases directly via a G(s) protein and decreases Ca(2+) current. ATP activates the inward-rectifying currents (ACh- and ATP-activated K(+) currents) and outward K(+) currents. P2-purinergic stimulation increases cAMP by activating adenylyl cyclase isoform V. It also involves tyrosine kinases to activate phospholipase C-gamma to produce inositol 1,4,5-trisphosphate and Cl(-)/HCO(3)(-) exchange to induce a large transient acidosis. No clear correlation is presently possible between an effect and the activation of a given P2-receptor subtype in cardiomyocytes. ATP itself is generally a positive inotropic agent. Upon rapid application to cells, ATP induces various forms of arrhythmia. At the tissue level, arrhythmia could be due to slowing of electrical spread after both Na(+) current decrease and cell-to-cell uncoupling as well as cell depolarization and Ca(2+) current increase. In as much as the information is available, this review also reports analog effects of UTP and diadenosine polyphosphates.
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PMID:Adenosine 5'-triphosphate: a P2-purinergic agonist in the myocardium. 1127 44

We determined whether activation of G proteins can affect the force developed for a given intracellular Ca(2+) concentration ([Ca(2+)]; i.e., the Ca(2+) sensitivity) by mechanisms in addition to changes in regulatory myosin light chain (rMLC) phosphorylation. Responses in alpha-toxin-permeabilized canine tracheal smooth muscle were determined with Ca(2+) alone or in the presence of ACh, endothelin-1 (ET-1), or aluminum fluoride (AlF; acute or 1-h exposure). Acute exposure to each compound increased Ca(2+) sensitivity without changing the response to high [Ca(2+)] (maximal force). However, chronic exposure to AlF, but not to chronic ACh or ET-1, increased maximal force by increasing the force produced for a given rMLC phosphorylation. Studies employing thiophosphorylation of rMLC showed that the increase in force produced by chronic AlF exposure required Ca(2+) during activation to be manifest. Unlike the acute response to receptor agonists, which is mediated solely by increases in rMLC phosphorylation, chronic direct activation of G proteins further increases Ca(2+) sensitivity in airways by additional mechanisms that are independent of rMLC phosphorylation.
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PMID:Calcium sensitization produced by G protein activation in airway smooth muscle. 1150 90

The increase in intracellular Ca(2+) and myosin light chain (MLC) phosphorylation in response to the contractile activation of tracheal smooth muscle is greater at longer muscle lengths (21). However, MLC phosphorylation can also be stimulated by Ca(2+)-insensitive signaling pathways (19). The cytoskeletal proteins paxillin and focal adhesion kinase (FAK) mediate a Ca(2+)-independent length-sensitive signaling pathway in tracheal smooth muscle (30). We used alpha-toxin-permeabilized tracheal smooth muscle strips to determine whether the length sensitivity of MLC phosphorylation can be regulated by a Ca(2+)-insensitive signaling pathway and whether the length sensitivity of active tension depends on the length sensitivity of myosin activation. Although active tension remained length sensitive, ACh-induced MLC phosphorylation was the same at optimal muscle length (L(o)) and 0.5 L(o) when intracellular Ca(2+) was maintained at pCa 7. MLC phosphorylation was also the same at L(o) and 0.5 L(o) in strips stimulated with 10 microM Ca(2+). In contrast, the Ca(2+)-insensitive tyrosine phosphorylation of FAK and paxillin stimulated by ACh was higher at L(o) than at 0.5 L(o). We conclude that the length-sensitivity of MLC phosphorylation depends on length-dependent changes in intracellular Ca(2+) but that length-dependent changes in MLC phosphorylation are not the primary mechanism for the length sensitivity of active tension.
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PMID:Selected contribution: roles of focal adhesion kinase and paxillin in the mechanosensitive regulation of myosin phosphorylation in smooth muscle. 1150 48

1. We have investigated the effect of U73122, a specific inhibitor of phospholipase C (PLC), on acetylcholine-activated K(+) currents (I(KACh)) in mouse atrial myocytes. 2. In perforated patch clamp mode, I(KACh) was activated by 10 microM acetylcholine. When atrial myocytes were pretreated with U73122 or U73343, I(KACh) was inhibited dose-dependently (half-maximal inhibition at 0.12+/-0.0085 and 0.16+/-0.0176 microM, respectively). The current-voltage relationships for I(KACh) in the absence and in the presence of U73122 showed that the inhibition occurred uniformly from -120 to +40 mV, indicating a voltage-independent inhibition. 3. When U73122 was applied after I(KACh) reached steady-state, a gradual decrease in I(KACh) was observed. The time course of the current decrease was well fitted to a single exponential, and the rate constant was proportional to the concentration of U73122. 4. When K(ACh) channels were directly activated by adding 1 mM GTP gamma S to the bath solution in inside-out patches, U73122 (1 microM) decreased the open probability significantly without change in mean open time. When K(ACh) channels were activated independently of G-protein activation by 20 mM Na(+), open probability was also inhibited by U73122. 5. Voltage-activated K(+) currents and inward rectifying K(+) currents were not affected by U73122. 6. These findings show that inhibition by U73122 and U73343 of K(ACh) channels occurs at a level downstream of the action of G beta gamma or Na(+) on channel activation. The interference with phosphatidylinositol 4,5-bisphosphate (PIP(2))-channel interaction can be suggested as a most plausible mechanism.
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PMID:Inhibition of acetylcholine-activated K(+) currents by U73122 is mediated by the inhibition of PIP(2)-channel interaction. 1168 55

Regulation of glucose metabolism by cholinergic nervous activation has been demonstrated. In an attempt to evaluate the role of cholinergic receptor subtype in this regulation of glucose metabolism, we employed cultured myoblast C2C12 cells to investigate the glucose uptake in the present study. Acetylcholine (ACh) enhanced the uptake of radioactive glucose into C2C12 cells at the concentration range of 0.001 to 1.0 micromol/l. This effect was suppressed by the muscarinic antagonist atropine. Effect of ACh on muscarinic receptors was further supported by the blockade of scopolamine, another classical antagonist. Thus, activation of muscarinic receptors to enhance the radioactive glucose uptake into C2C12 cells can be considered. Moreover, pirenzepine, the antagonist of muscarinic M1 receptors, competitively antagonized the action of ACh in C2C12 cells. However, methoctramine at concentration sufficient to inhibit the muscarinic M2 receptors failed to produce similar effect. Similarly, 4-DAMP at effective concentration to block muscarinic M3 receptors lacked the influence. An activation of muscarinic M1 receptors seems responsible for the action of ACh in C2C12 cells. Pharmacological inhibition of phospholipase C by U73312 resulted in a concentration-dependent decrease in ACh-stimulated uptake of radioactive glucose into C2C12 cells. However, treatment with U73343, the inactive congener, failed to block the action of ACh. Moreover, both chelerythrine and GF 109203X diminished the action of ACh at concentrations sufficient to inhibit protein kinase C. Therefore, the obtained data suggest that increase of the glucose uptake evoked by ACh is mainly due to the activation of muscarinic M1 receptors in cultured myoblast C2C12 cells.
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PMID:Activation of muscarinic M1 receptors by acetylcholine to increase glucose uptake into cultured C2C12 cells. 1195 76

Depletion of phosphatidylinositol 4,5-bisphosphate (PIP(2)) induced by phenylephrine or endothelin causes the inhibition of acetylcholine-activated K(+) current (I(KACh)) in atrial myocytes. In the present study, we have investigated the hypothesis that muscarinic receptor induced PIP(2) depletion also causes inhibition of I(KACh), resulting in desensitization. We confirmed the expression of G(q)-coupled muscarinic receptors in mouse atrial myocytes using reverse transcriptase-polymerase chain reaction. The involvement of M(1) and M(3) receptors in desensitization is examined using specific antagonists, 4-DAMP and pirenzepine, but they significantly reduced peak I(KACh), implying nonspecific M(2) blockade. When ACh-induced phosphoinositide depletion was specifically inhibited using PLCbeta1 knock-out mice, the extent of desensitization during 4 min was 47.5 +/- 3.2%, which was not different from that in wild type (46.8 +/- 2.1%). Phenylephrine-induced phosphoinositide hydrolysis and phenylephrine-induced inhibition of I(KACh) were not affected by PLCbeta1 knock-out. To facilitate PIP(2) depletion, replenishment of PIP(2) was blocked by wortmannin. Wortmannin did not affect the desensitization and the recovery from desensitization. These results suggest that PIP(2) depletion by acetylcholine does not contribute to short-term desensitization of I(KACh). The differential regulation of I(KACh) by different phospholipase C-linked receptors may imply that receptor co-localization is required for PIP(2) to act as a signaling molecule.
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PMID:Acetylcholine-induced phosphatidylinositol 4,5-bisphosphate depletion does not cause short-term desensitization of G protein-gated inwardly rectifying K+ current in mouse atrial myocytes. 1201 67

This study was designed to determine whether lipoxygenase-dependent metabolites of arachidonic acid are involved in the endothelium-dependent hyperpolarization of the guinea pig carotid artery. The membrane potential of vascular smooth muscle cells was measured with intracellular microelectrodes and potassium channels were studied on freshly isolated cells with the patch-clamp technique. Acetylcholine-induced hyperpolarizations were not affected by arachidonyl trifluoromethyl ketone (AACOCF3), quinacrine (phospholipase A inhibitors), or eicosatetraenoic acid (nonspecific inhibitor of lipoxygenase, cytochrome P450, and cyclooxygenase). In contrast, cinnamyl-3,4 dihydroxy-alpha-cyanocinnamate (CDC) and AA861 (lipoxygenase inhibitors) as well as 1-(6-(17beta-3-methoxyestra-1,3,5(10)-trien-17-yl)amino) hexyl)-1H-pyrrole-2,5-dione (U-73122) (phospholipase C inhibitor) produced a significant inhibition of the hyperpolarization. An opener of intermediate conductance calcium-activated potassium channels, 1-ethyl-2-benzamidazolinone (1-EBIO), induced a hyperpolarization that was unaffected by AACOCF3, CDC, AA861, or U-73122 but was inhibited by charybdotoxin. (+/-)12-hydroxy-eicosatetraenoic acid (12-HETE) and 12(S)-hydroperoxy-eicosatetraenoic acid (12(S)-HpETE) did not induce any significant changes in membrane potential. CDC inhibited the voltage-gated potassium current and increased the large conductance calcium-activated potassium current whereas AA861 inhibited both potassium currents. These results confirm that, in the isolated carotid artery of the guinea pig, stimulation of endothelial muscarinic receptors involves phospholipase C activation and indicate that the activation of phospholipase A2 and the release of lipoxygenase metabolites is unlikely to explain endothelium-dependent hyperpolarization.
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PMID:Endothelium-dependent hyperpolarization to acetylcholine in carotid artery of guinea pig: role of lipoxygenase. 1219 33

Peristaltic contractions in the stomach are regulated by the spread of electrical slow waves from the corpus to the pylorus. Gastric slow waves are generated and propagated by the interstitial cells of Cajal (ICC). All regions distal to the dominant pacemaker area in the corpus are capable of generating slow waves, but orderly gastric peristalsis depends upon a frequency gradient in which the corpus pacemaker frequency exceeds the antral frequency. Cholinergic, muscarinic stimulation enhances pacemaker frequency. We investigated this phenomenon using intact murine gastric muscles and cultured ICC. Acetylcholine (ACh) increased the frequency of slow waves in antrum and corpus muscles. The increase was significantly greater in the antrum. ACh and carbachol (CCh) increased the pacemaker currents in cultured ICC. At high doses of CCh, transient pacemaker currents fused into sustained inward currents that persisted for the duration of stimulation. The effects of CCh were blocked by low doses of the M(3) receptor antagonist 1-dimethyl-4-diphenylacetoxypiperidinium. Frequency enhancement by CCh was not affected by forskolin, but the phospholipase C inhibitor U-73122 inhibited both the increase in frequency and the development of tonic inward currents. 2-Aminoethyldiphenyl borate also blocked the chronotropic responses to CCh. Inhibitors of protein kinase C did not block responses to CCh. These studies show that mice are an excellent model for studying mechanisms that regulate gastric slow-wave frequency. CCh, apparently via production of inositol 1,4,5-trisphosphate, accelerates the frequency of pacemaker activity. High concentrations of CCh may block the entrainment of pacemaker currents, resulting in a tonic inward current.
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PMID:Muscarinic regulation of pacemaker frequency in murine gastric interstitial cells of Cajal. 1252 28

Within muscular equivalents of cat lower esophageal sphincter (LES), the circular muscle develops greater spontaneous tone, whereas the sling muscle is more responsive to cholinergic stimulation. Smooth muscle contraction involves a combination of calcium release from stores and of calcium entry via several pathways. We hypothesized that there are differences in the sources of Ca(2+) used for contraction in sling and circular muscles and that these differences could contribute to functional asymmetry observed within LES. Contraction of muscle strips from circular and sling regions of LES was assessed in the presence of TTX. In Ca(2+)-free Krebs, tone was inhibited to a greater degree in circular than sling muscle. L-type Ca(2+) channel blockade with nifedipine or verapamil inhibited tone in LES circular but not sling muscle. Sarcoplasmic reticulum (SR) Ca(2+)-ATPase inhibitor cyclopiazonic acid (CPA) caused greater increase in tone in sling than in circular muscle. The phospholipase C inhibitor U-73122 and the SR inositol 1,4,5-trisphosphate [Ins(1,4,5)P(3)] receptor blocker 2-aminoethoxydiphenyl borate (2-APB) inhibited tone in circular and sling muscles, demonstrating that continuous release of Ca(2+) from Ins(1,4,5)P(3)-sensitive stores is important in tone generation in both muscles. In Ca(2+)-free Krebs, ACh-induced contractions (AChC) were inhibited to a greater degree in sling than circular muscles. However, nifedipine and verapamil greatly inhibited AChC in the circular but not sling muscle. Depletion of SR Ca(2+) stores with CPA or inhibition of Ins(1,4,5)P(3)-mediated store release with either U-73122 or 2-APB inhibited AChC in both muscles. We demonstrate that LES circular and sling muscles 1) use intracellular and extracellular Ca(2+) sources to different degrees in the generation of spontaneous tone and AChC and 2) use different Ca(2+) entry pathways. These differences hold the potential for selective modulation of LES tone in health and disease.
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PMID:Calcium source diversity in feline lower esophageal sphincter circular and sling muscle. 1456 70


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