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)

The cellular mechanisms underlying the clinical effects of volatile anaesthetics remain unknown, although the plasma membrane and its associated proteins are likely targets. One such protein is the enzyme phospholipase C (PLC), which catalyses the formation of the second messenger inositol(1,4,5)triphosphate [Ins(1,4,5)P3]. Using SH-SY5Y human neuroblastoma cells we have demonstrated that halothane (0.50, 0.75 and 1.00%) enhances basal Ins(1,4,5)P3 mass formation approximately 1.8-fold. Halothane also caused a dose-dependent enhancement of carbachol-stimulated biphasic Ins(1,4,5)P3 formation at both the peak (half-maximal stimulation, EC50 = 0.76%) and plateau (EC50 = 0.74%) phases. At 1%, halothane did not alter the affinity for carbachol at either the peak (IC50: air = 9.4 +/- 1.5, halothane = 12.7 +/- 1.0 microM) or plateau (EC50: air = 11.7 +/- 1.2, halothane = 11.6 +/- 1.0 microM) phase, but did increase the maximum Ins(1,4,5)P3 response at both phases (air vs halothane: peak, 79.9 +/- 0.5 vs 124.8 +/- 2.5; plateau, 33.2 +/- 0.5 vs 47.9 +/- 0.6 pmol/mg protein). Isoflurane (2%) also enhanced basal and carbachol-stimulated Ins(1,4,5)P3 formation 2-fold and 1.5-fold, respectively. In summary, clinically relevant doses of the volatile anaesthetics halothane and isoflurane enhance basal and carbachol-stimulated Ins(1,4,5)P3 formation. Thus, activation of PLC, and subsequent potential Ins(1,4,5)P3-mediated rises in intracellular calcium, could play a part in the cellular mechanisms of volatile agent-induced anaesthesia.
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PMID:Halothane and isoflurane enhance basal and carbachol-stimulated inositol(1,4,5)triphosphate formation in SH-SY5Y human neuroblastoma cells. 814 13

In this study I attempted to elucidate the depressant effects of volatile anesthetics on inositol trisphosphate (IP3)-mediated signal transduction pathway and to identify the site of action. For this purpose, we used Xenopus laevis oocytes which translated and expressed 5-HT receptors after injection of mRNA isolated from the rat brain. In this system, binding of the agonist to G-protein coupled receptors activates phospholipase C that produces IP3. Mobilization of Ca2+ by IP3 from the storage finally opens Ca2+ dependent Cl- channels. Halothane, isoflurane and methoxyflurane depressed Cl- current elicited by 5-HT. For the further quantitative study, methoxyflurane was used because of its better solubility and less vapor pressure that avoided evaporation of the agent. The 5-HT elicited Cl- current was depressed in a non-competitive fashion. Response were 75, 60, 20% of control in the presence of 0.5, 1 and 3 mM methoxyflurane, respectively. Responses elicited by a pressure-injection of Ca2+ or IP3 remained unchanged in the presence of high concentrations of either halothane, isoflurane or methoxyflurane. These results suggest that the depressant mechanism by volatile anesthetics on the signal transduction pathway involves neither Ca2+ dependent Cl- channel dynamics nor intracellular Ca2+ mobilization by IP3. Changes of microdomain characteristics of the membrane in the presence of anesthetic molecules including membrane-bound proteins and enzyme system may be a main mechanism of action of volatile anesthetics.
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PMID:[Depressant effects of volatile anesthetics on second messenger system in mRNA-expressed Xenopus laevis oocytes]. 815 57

The ability of halothane to stimulate phospholipase C (PLC) was examined in turkey erythrocyte membranes prepared from [3H]inositol-labeled turkey erythrocytes by measuring [3H]inositol phosphate formation ([3H]InsP) in the presence and absence of G-protein activation. In the presence of guanosine 5'-3-O-(thio)triphosphate) (GTP gamma S), halothane (0.5-10 mM) caused a dose-dependent activation of PLC. The EC50 value for halothane-induced PLC activation was 2.8 +/- 0.3 mM. Halothane (0.1-30 mM) had no effect on PLC activity in the absence of G-protein activation and did not affect Ca(2+)-dependent PLC activity. The activation of PLC by GTP gamma S occurred after an initial lag period of 60 s which was followed by a linear increase in [3H]InsP. Halothane dose-dependently decreased the lag period for GTP gamma S-induced PLC activation (minimal value 15 s) and increased the rate of [3H]InsP formation at all time points following this lag. As a result, halothane shifted the EC50 value for GTP gamma S-induced PLC activation to the left (4-fold) and increased its maximal response. Halothane also caused a dose-dependent activation of PLC in the presence of AlF4-. Half-maximal stimulation of AlF4(-)-activated PLC occurred with an EC50 value of 2.9 +/- 0.4 mM halothane, which is similar to the halothane dose giving half-maximal stimulation of PLC in the presence of GTP gamma S. At low doses (0.1-0.3 mM) halothane inhibited both isoproterenol- and adenosine 5'-O-(2-thiodiphosphate) (ADP beta S)-induced [3H]InsP formation, whereas at higher concentrations it stimulated PLC independent of the presence of these agonists. At concentrations chosen to reflect their different membrane/buffer partition coefficients, both hexanol (5 mM) and benzyl alcohol (20 mM) fluidized turkey erythrocyte membranes to the same degree as halothane (5 mM). However, these agents had no effect on GTP gamma S- or AlF(4-)-induced PLC activity, indicating that halothane-induced PLC activation was not secondary to changes in bulk lipid fluidity properties. Halothane also stimulated [3H]inositol bisphosphate and [3H]inositol trisphosphate formation in intact erythrocytes. These data demonstrate that the anesthetic halothane can stimulate G-protein-dependent PLC activity and modify the responsiveness of this signaling system to activation by receptor-linked agonists.
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PMID:Halothane regulates G-protein-dependent phospholipase C activity in turkey erythrocyte membranes. 834 Mar 82

Indo-1 and fluo-3 imaging techniques were used to investigate the role of gap junctions in the changes in cytosolic calcium concentrations ([Ca2+]i) induced by several receptor agonists. Subpopulations of confluent cultured astrocytes from the rat striatum were superfused with submaximal concentrations of endothelin-1 (Et1) and the alpha 1-adrenergic and muscarinic receptor agonists, methoxamine and carbachol, respectively. 2. Combined binding and autoradiographic studies indicated that all striatal astrocytes possess binding sites for Et1. In contrast, alpha 1-adrenergic and muscarinic binding sites were found to be heterogeneously distributed. In agreement with these findings, Et1 induced fast calcium responses in all cells while only subsets of striatal astrocytes responded to the application of methoxamine or carbachol. 3. Halothane, heptanol and octanol, which are commonly used as gap junction inhibitors, drastically reduced the amplitude of Et1-induced calcium responses. In contrast, 18-alpha-glycyrrhetinic acid (alpha GA) used at a concentration known to block gap junction permeability in astrocytes had no significant effect on the amplitude of these calcium responses. 4. As demonstrated by quantitative and topological analysis, Et1 application similarly increased [Ca2+]i levels in all astrocytes in both the absence and presence of alpha GA. 5. In control conditions, subpopulations of cells responding to methoxamine or carbachol exhibited two main types of calcium responses which differed in their shape and kinetic characteristics. In the presence of alpha GA the number of cells responding to these receptor agonists was significantly reduced. Indeed, responses characterized by their long latency, slow rise time and weak amplitude disappeared in the presence of alpha GA while responses with short latency and fast rise time were preserved. 6. These results indicate that permeable gap junction channels tend to attenuate the pharmacological and functional heterogeneity of populations of astrocytes, while their inhibition restricts calcium responses in astrocytes expressing high densities of transmitter receptors coupled to phospholipase C.
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PMID:Gap junctional communication and pharmacological heterogeneity in astrocytes cultured from the rat striatum. 970 94

Since volatile anesthetics inhibited high voltage-gated calcium channels and G-protein-coupled M(1) muscarinic signaling, their effects upon M(1) receptor-induced modulation of L-type (alpha1C) calcium channel was investigated. Voltage-clamped Ba(2+) currents (I(Ba)) were measured in Xenopus oocytes coexpressed with L-type channels and M(1) muscarinic receptors. M(1) receptor agonist, acetyl-beta-methylcholine (MCh) inhibited the peak and late components of I(Ba) in a dose-dependent manner. Analysis of I(Ba) after the treatment with MCh or volatile anesthetics revealed that the inactivating component, its time constant, and the noninactivating current were all decreased by these agents. MCh-induced inhibition followed a second messenger pathway that included G-proteins, phospholipase C, inositol-1,4,5-trisphosphate, and intracellular calcium [Ca(2+)](i). Although halothane or isoflurane inhibited I(Ba,) their effect was not mediated through these intracellular second messengers. By using volatile anesthetics and MCh sequentially, and in various combinations, the susceptibility of L-type currents and their modulation by M(1) receptors to volatile anesthetics were investigated. When MCh and volatile anesthetics were administered together simultaneously, a pronounced inhibition that was approximately equal to the sum of their individual effects was seen. Halothane or isoflurane further inhibited the I(Ba) when either volatile anesthetic was administered following the inhibition produced by prior administration of MCh. However, when MCh was administered following either volatile anesthetic, its effect was significantly reduced. Thus, whereas volatile anesthetics appear to directly inhibit L-type channels, they also interfere with channel modulation by G-protein-coupled receptors, which may have functional implications for both neuronal and cardiovascular tissues.
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PMID:Differential sensitivity of expressed L-type calcium channels and muscarinic M(1) receptors to volatile anesthetics in Xenopus oocytes. 1135 20