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 effects of MgADP and inorganic phosphate (Pi) on cross-bridge detachment were determined in tonic (rabbit femoral artery) and phasic (rabbit bladder and guinea pig portal vein) smooth muscles permeabilized with staphylococcal alpha-toxin. Relaxation from rigor was induced by photolysis of ATP (1.2-1.5 mM) from caged ATP. The initial one second of relaxation from rigor was resolved into two exponential components: a rapid component with normalized amplitudes, Af, of 8, 15 and 26% and rate constants, kf (in s-1) of 26, 36 and 30 in rabbit femoral artery, guinea pig portal vein, and rabbit bladder; the respective rate constants of the second, slower component, ks, were 0.07, 0.2 and 0.1. Removal of residual endogenous ADP with apyrase treatment increased the amplitude Af and accelerated ks; addition of MgADP reduced Af. The combination of these effects (increases in Af and ks) decreased the t1/2 of relaxation from control values by factors of 2.6 (femoral artery), 6.7 (portal vein) and 10 (bladder). Pi (30 mM) further increased the amplitudes Af. The affinity of MgADP for myosin cross-bridges, estimated as the reduction of the relative amplitude of the rapid component, Af, was significantly higher in tonic than in phasic smooth muscle: the KD of MgADP was 1.1 +/- 0.3 microM in rabbit femoral artery and 4.9 +/- 1.0 microM in rabbit bladder. The higher affinity of tonic smooth muscle myosin for MgADP correlated with its relatively high LC17b isoform content (58 +/- 4.2%) in contrast to the lower affinity of the phasic, bladder detrusor smooth muscle that contained only the LC17a isoform.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Flash photolysis studies of relaxation and cross-bridge detachment: higher sensitivity of tonic than phasic smooth muscle to MgADP. 812 26

Thromboxane A2 (TXA2) is a potent, labile vasoconstrictor which stimulates vessel contraction through vascular smooth muscle TXA2 receptors differing from those in platelets. We studied TXA2-stimulated events in cultured adult rat aortic smooth muscle cells. The stable TXA2 mimetic (15S)-hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5Z, 13E-dienoic acid (U46619) competed for TXA2 agonist binding to vascular smooth muscle cells with an IC50 of 10 +/- 1 nM. In fura-2-loaded cells, U46619 increased free cytosolic Ca++ concentration with an EC50 of 49 +/- 14 nM. The increase in free cytosolic Ca++ was rapid, transient and independent of extracellular Ca++ or Ca++ antagonists and thus was due to release from intracellular stores. U46619-mediated Ca++ release was temporally associated with phosphorylation of myosin light chains, increased accumulation of 1,4,5-inositol trisphosphate (EC50 = 32 +/- 4 nM) and cytoplasmic acidification from pH 7.06 +/- 0.01 to 7.00 +/- 0.02 (P = .02). Ca++ release was 53% attenuated by the phospholipase C inhibitor, 1-[6-[[17 beta-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H- pyrrole-2,5-dione. In rat aortic rings U46619 caused TXA2 receptor-mediated contractions (EC50 of 28 +/- 2 nM) which were not attenuated by removal of extracellular Ca++ from the superfusion buffer. Together, these results suggest that agonist occupation of TXA2 receptors produces vascular smooth muscle contraction through initial activation of phospholipase C with production of 1,4,5-inositol phosphate, release of intracellular calcium stores and phosphorylation of myosin light chains associated with cellular acidification, presumably via activation of Ca++ ATPase.
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PMID:Thromboxane A2 stimulated signal transduction in vascular smooth muscle. 847 27

The adenosine analog, N-ethylcarboxamidoadenosine (NECA), causes transient activation of phospholipase C and an enhancement of antigen-induced secretion in a rat mast cell (RBL-2H3) line via adenosine A3-receptors (Ramkumar et al., J. Biol. Chem. 268:16887, 1993) by a mechanism that is inhibited by bacterial toxins and potentiated by dexamethasone (Ali et al., J. Biol. Chem. 265:745-753, 1990). Here we show that NECA synergizes the secretory response to Ca(2+)-ionophore as well as to antigen. The ability of NECA to synergize the secretory responses persisted for 10 to 20 min, long after the early phospholipase C-mediated reactions to NECA had subsided. NECA caused, however, a dose-dependent sustained activation of phospholipase D, as indicated by the formation of [3H]phosphatidic acid, or in the presence of 0.3% ethanol, [3H]phosphatidylethanol. This activation was associated with a sustained increase in diglycerides, in protein kinase C activity and in the phosphorylation of myosin light chains by protein kinase C. The generation of diglycerides was enhanced in dexamethasone-treated cells and suppressed in cells that had been treated with cholera toxin or pertussis toxin. Collectively, the studies suggested that the generation of diglycerides via phospholipase D and the associated activation of protein kinase C were, by themselves, insufficient signals for secretion in RBL-2H3 cells, but that these reactions synergized responses to stimulants such as antigen or A23187 that caused substantial increases in [Ca2+]i.
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PMID:Sustained activation of phospholipase D via adenosine A3 receptors is associated with enhancement of antigen- and Ca(2+)-ionophore-induced secretion in a rat mast cell line. 863 57

Parturition results from the establishment of phasic regular uterine contractions. Contractility in myometrial smooth muscle is stimulated by an increase in intracellular calcium ([Ca2+i]) which activates myosin light chain phosphorylation leading to increased myosin ATPase activity and enhanced rate of acto-myosin cross bridge formation. G proteins play a pivotal role in smooth muscle activation and relaxation by coupling cell membrane receptors to effector enzymes and ion channels. G alpha(s) and G alpha(i) stimulate and inhibit adenylyl cyclase, respectively and control cAMP formation. G alpha(q) stimulates phospholipase C resulting in the formation of two second messengers: inositol 1,4,5-trisphosphate (InsP3) which releases Ca2+ from the sarcoplasmic reticulum, and 1,2-diacylglycerol which activates protein kinase C. The oxytocin receptor stimulates myometrial contractility by increasing [Ca2+i] through both pertussis toxin resistant (G alpha(q)) and pertussis toxin sensitive (?G alpha (i)) pathways. beta-Adrenoceptors and prostaglandin EP2 receptors promote relaxation via G alpha(s)-adenylyl cyclase. The concentration of myometrial oxytocin receptors is five-times higher in pregnant compared to non-pregnant myometrium but decreases in samples obtained during labour. When myometrial slices are challenged with oxytocin there is a rapid increase in InsP3 levels with a time course which is similar to the rise in [Ca2+i] provoked by oxytocin in cultured myometrial cells. The formation of InsP3 in response to oxytocin in myometrial tissue at term is similar in samples obtained before and after the onset of labour. G alpha(q) and G alpha(i) are expressed at similar levels in non-pregnant and in pregnant myometrium obtained before or during labour. By contract, G alpha(s) levels are higher in pregnant compared to non-pregnant myometrium and decrease in samples obtained during labor. These changes in G alpha(s) are paralleled by prostaglandin E2-induced adenylyl cyclase activity in the same tissues. Parturition may be the consequence of downregulation of pathways that favour uterine quiescence by increasing cAMP formation, resulting in a relative dominance of stimulatory receptors that increase InsP3/Ca2+ availability.
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PMID:Parturition: activation of stimulatory pathways or loss of uterine quiescence? 871 97

The chemoattractant cAMP induces directed cell locomotion in Dictyostelium cells. Several second messenger pathways are activated upon binding of cAMP to G-protein-coupled receptors, including adenylyl cyclase, guanylyl cyclase, phospholipase C, and the opening of plasma membrane Ca2+ channels. These second messenger responses are unaltered in many chemotactic mutants, except for the cGMP response. Activation of guanylyl cyclase depends on G-proteins and is regulated by a cGMP-binding protein in a complex manner. This cGMP-binding protein also mediates intracellular functions of cGMP to activate a PKC-related kinase that phosphorylates myosin II heavy chain, thereby allowing myosin filaments to rearrange during cell movement.
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PMID:cGMP as second messenger during Dictyostelium chemotaxis. 924 16

1. The effect of thiophosphorylation of the regulatory myosin light chain (MLC20) on rigor stiffness was determined in permeabilized rabbit bladder smooth muscle. 2. Rigor stiffness of alpha-toxin-permeabilized smooth muscle was significantly increased by thiophosphorylation of MLC20. This increase may have been due to partial shortening (melting) in the proximal rod region and/or stiffening of the regulatory domain of the myosin head. 3. We suggest that phosphorylation of MLC20, by increasing the stiffness of the S1 lever arm and/or S2 hinge regions of the myosin molecule, favours separation of the two phosphorylated heads and consequent deinhibition of motor domain activity.
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PMID:Thiophosphorylation of myosin light chain increases rigor stiffness of rabbit smooth muscle. 976 25

Intracellular movement of secretory granules is a proximal stage in the secretory cascade that ends in the release product from cells. We investigated mechanisms underlying the control of this movement by acetylcholine using an insulinoma cell line, MIN6, in which acetylcholine increases both insulin secretion and granule movement. The peak activation of movement was observed 3 min after an acetylcholine challenge. The effects were nullified by the muscarinic inhibitor atropine, phospholipase C (PLC) inhibitors (D 609 and compound 48/80), and pretreatment with the Ca2+ pump inhibitor, thapsigargin. Inhibitors of Ca2+-dependent phospholipase A2 (arachidonyl trifluoromethyl ketone and methyl arachidonyl fluorophosphate) also partially inhibited the movement caused by acetylcholine, but downregulation of protein kinase C by overnight incubation with the phorbol ester 12-o-tetradecanoylphorbol-13-acetate failed to exert any influence. Acetylcholine stimulation of granule movement was not reproduced by membrane depolarization with high K+. Phosphorylation of the endogenous myosin light chain in MIN6 cells was increased by addition of acetylcholine and decreased by the Ca2+ chelator BAPTA (1,2-bis[2-aminophenoxy]ethane-N,N,N',N'-tetraacetic acid). The calmodulin inhibitor W-7 and the myosin light-chain kinase inhibitor ML-9 decreased the motile events in the beta-cells under both nonstimulated and acetylcholine-stimulated conditions. These findings led us to conclude that inositol trisphosphate [corrected] causes Ca2+ mobilization by muscarinic activation of PLC, leading to intracellular translocation of insulin granules to the ready-releasable pool in pancreatic beta-cells via Ca2+/calmodulin-dependent phosphorylation of myosin light chains.
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PMID:Acetylcholine activates intracellular movement of insulin granules in pancreatic beta-cells via inositol trisphosphate-dependent [correction of triphosphate-dependent] mobilization of intracellular Ca2+. 979 38

Neurohumoral stimulation of smooth muscle leads to an increased responsiveness of the myofilaments to Ca2+. This review provides a summary of the data that suggest that the signalling from the membrane-bound serpentine receptors to the contractile apparatus leading to the increase in Ca(2+)-sensitivity requires the activation of the Ras-related low molecular mass GTPase Rho. In smooth muscle permeabilized with alpha-toxin or beta-escin, the increase in force elicited by different agonists at fixed [Ca2+] (Ca(2+)-sensitization) can be inhibited by bacterial toxins (EDIN, and exoenzyme C3) which ADP-ribosylate and inactivate Rho proteins. Moreover, the agonist-induced increase in Ca(2+)-sensitivity can be mimicked by constitutively active recombinant Rho proteins. The physiological relevance of this mechanism is suggested by the fact that toxins that are internalized into intact cells (toxin B from C. difficile and a chimeric toxin (DC3B) consisting of C3 and the (non-catalytic) B fragment of diphteria toxin (inhibit the tonic phase of an agonist-induced contraction. Toxin B inhibits contraction without affecting the intracellular Ca(2+)-transient determined with fura-2. However, it inhibits phosphorylation of the regulatory light chains of myosin (MLC). Rho has been suggested to activate a Rho-associated kinase which in turn phosphorylates the myosin binding subunit of the myosin light chain phosphatase. This would lead to an increase in phosphorylation of MLC and hence of force at constant Ca2+. The Ca(2+)-sensitizing effect of agonists is also inhibited by tyrosine kinase inhibitors. This suggests the possibility that in smooth muscle, like in non-muscle cells, there is a cross-talk between Rho and tyrosine kinases.
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PMID:Involvement of small GTPases in the regulation of smooth muscle contraction. 988 68

We have investigated the possibility that ET-1 can induce an increase in myofilament calcium sensitivity in pulmonary artery smooth muscle. Arterial rings were permeabilized using alpha-toxin (120 microg ml(-1)), in the presence of A23187 (10 microM) to 'knock out' Ca2+ stores, and pre-constricted with pCa 6.8 (buffered with 10 mM EGTA). In the presence of this fixed Ca2+ concentration, 1 microM ET-1 induced a sustained, reversible constriction of 0.15 mN. Pulmonary arterial rings were freeze-clamped at the peak of the induced constriction (time matched). Subsequent densitometric analysis revealed that ET-1 (1 microM) increased the level of phosphorylated myosin light chains by 34% compared to an 11% increase in the presence of pCa 6.8 alone. In contrast to ET-1, the selective ET(B) receptor agonist Sarafotoxin S6C (100 nM) failed to induce a significant constriction. The constriction induced by 1 microM ET-1 was reversibly inhibited when the preparation was preincubated (15 min) with the ETA receptor antagonist BQ 123 (100 microM). The constriction measured 0.13 mN in the absence and 0.07 mN in the presence of 100 microM BQ 123. In contrast, the constriction induced by 1 microM ET-1 measured 0.19 mN in the absence and 0.175 mN following a 15 min pre-incubation with the ET(B) antagonist BQ 788 (100 microM). The constriction induced by 1 microM ET-1 measured 0.14 mN in the presence and 0.13 mN following pre-incubation with the tyrosine kinase inhibitor Tyrphostin A23 (100 microM). We conclude that ET-1 induced an increase in myofilament calcium sensitivity in rat pulmonary arteries via the activation of ET(A) receptors and by a mechanism(s) independent of tyrosine kinase.
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PMID:ET(A) receptors are the primary mediators of myofilament calcium sensitization induced by ET-1 in rat pulmonary artery smooth muscle: a tyrosine kinase independent pathway. 1036 68

Phototransduction in Drosophila is mediated by a G-protein-coupled phospholipase C transduction cascade in which each absorbed photon generates a discrete electrical event, the quantum bump. In whole-cell voltage-clamp recordings, cAMP, as well as its nonhydrolyzable and membrane-permeant analogs 8-bromo-cAMP (8-Br-cAMP) and dibutyryl-cAMP, slowed down the macroscopic light response by increasing quantum bump latency, without changes in bump amplitude or duration. In contrast, cGMP or 8-Br-cGMP had no effect on light response amplitude or kinetics. None of the cyclic nucleotides activated any channels in the plasma membrane. The effects of cAMP were mimicked by application of the non-specific phosphodiesterase inhibitor IBMX and the adenylyl cyclase activator forskolin; zaprinast, a specific cGMP-phosphodiesterase inhibitor, was ineffective. Bump latency was also increased by targeted expression of either an activated G(s) alpha subunit, which increased endogenous adenylyl cyclase activity, or an activated catalytic protein kinase A (PKA) subunit. The action of IBMX was blocked by pretreatment with the PKA inhibitor H-89. The effects of cAMP were abolished in mutants of the ninaC gene, suggesting this nonconventional myosin as a possible target for PKA-mediated phosphorylation. Dopamine (10 microM) and octopamine (100 microM) mimicked the effects of cAMP. These results indicate the existence of a G-protein-coupled adenylyl cyclase pathway in Drosophila photoreceptors, which modulates the phospholipase C-based phototransduction cascade.
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PMID:Modulation of the light response by cAMP in Drosophila photoreceptors. 1051 99


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