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Results for “Inositol Phosphates”

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At least 937 records · Page 52Linked to original sources
PubMed1990

Cyclic GMP stimulates inositol phosphate production in cultured pituitary cells: possible implication to signal transduction.

Addition of the stable and permeable analog 8-bromo cyclic GMP (8-BR-cGMP) to myo-[2-3H]inositol prelabeled cultured rat pituitary cells results in enhanced formation of [3H]-myo-inositol monophosphate (IP1). The stimulatory effect of the cyclic nucleotide analog is additive to the effect of Li+, which accumulates IP1 via inhibition of inositol 1-monophosphatase, and also to the effect of gonadotropin releasing hormone (GnRH) which stimulates the formation of IP1, as well as that of inositol 1,4-bisphosphate (IP2) and inositol 1,4,5-trisphosphate (IP3) via enhanced hydrolysis of polyphosphoinositides. Many Ca2(+)-mobilizing hormones acting via phosphoinosite turnover also stimulate cGMP formation. The cyclic nucleotide might then serve as a modulator by further hydrolysis of phosphoinositides needed for protein kinase C activation.

Animals↗
PubMed1987

Islet activating protein inhibits kinin-stimulated inositol phosphate production, calcium mobilization, and prostaglandin E2 synthesis in renal papillary collecting tubule cells independent of cyclic AMP.

The effects of islet-activating protein (pertussis toxin) on bradykinin-mediated inositol trisphosphate labeling, prostaglandin E2 production, and calcium mobilization in rabbit renal papillary collecting tubule cells were assessed. Islet-activating protein induced time and concentration-dependent decreases in bradykinin-stimulated prostaglandin E2 production. Islet-activating protein induced increases in basal cyclic AMP levels but not in arginine vasopressin-stimulated cAMP. This effect could be inhibited by prior incubation with 2',5'-dideoxyadenosine, an inhibitor of adenylate cyclase. Although cAMP and cAMP analogues were able to inhibit both basal and bradykinin-stimulated prostaglandin E2 formation, the inhibitory effects of islet-activating protein on prostaglandin E2 formation and inositol trisphosphate labeling were observed in the presence of dideoxyadenosine. Moreover, islet-activating protein lowered both the basal and kinin-stimulated cytosolic calcium concentration as assessed by Quin 2 fluorescence. Finally, incubation of a membrane fraction of papillary cells with islet-activating protein resulted in the ADP-ribosylation of a 39/41-kDa doublet. These data support the role of a guanine nucleotide regulatory protein in bradykinin-mediated signal transduction in rabbit papillary collecting tubule cells.

Adenosine Diphosphate Ribose↗
PubMed1989

How do inositol phosphates regulate calcium signaling?

Activation of a variety of cell surface receptors results in the phospholipase C-catalyzed hydrolysis of the minor plasma membrane phospholipid phosphatidylinositol 4,5-bisphosphate, with concomitant formation of inositol 1,4,5-trisphosphate and diacylglycerol. There is strong evidence that inositol 1,4,5-trisphosphate stimulates Ca2+ release from intracellular stores. The Ca2+-releasing actions of inositol 1,4,5-trisphosphate are terminated by its metabolism through two distinct pathways. Inositol 1,4,5-trisphosphate is dephosphorylated by a 5-phosphatase to inositol 1,4-bisphosphate; alternatively, inositol 1,4,5-trisphosphate can also be phosphorylated to inositol 1,3,4,5-tetrakisphosphate by a 3-kinase. Although the mechanism of Ca2+ mobilization is understood, the precise mechanisms involved in Ca2+ entry are not known; the proposal that inositol 1,4,5-trisphosphate secondarily elicits Ca2+ entry by emptying an intracellular Ca2+ pool is considered.

Animals↗
PubMedDate not supplied

Excitatory amino acid-induced inositol phosphate formation in cultured retinal pigment epithelium.

Excitatory amino acid (EAA)-induced production of inositolphosphates (IPs) was studied in primary cultures of chick retinal pigment epithelium (RPE) following in vitro incorporation of [3H] myo-inositol. Glutamic acid (L-glu) significantly increased [3H]-IPs accumulation (215%). L-glu agonists stimulated [3H]IPs accumulation in the following order of efficiency: N-methyl-D-aspartate (NMDA) > or = L-glu > quisqualate > or = kainate > (IS,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD). Stimulation was dependent on external Ca2+. The NMDA-induced response was blocked by (+)-5-methyl-10,11-dihydro-5H-dibenzo-cyclohepten-5,10-imine maleate (MK-801) and 3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP) and was decreased by the L-Ca2+-channel blockers verapamil and nifedipine as well as by dantrolene. The metabotropic glutamate receptor (mGluR) antagonist (+)-alpha-methyl-4-carboxyphenylglycine (+)MCPG inhibited 3,5-dihydroxyphenylglycine (DHPG) and ACPD-induced stimulation, which demonstrates the presence in RPE of mGluRs 1 and/or 5, as well as NMDA receptors coupled directly, or through the influx of external Ca2+, to phospholipase C activation. L-glu agonists showed no effect either on basal level of intracellular cyclic adenosine monophosphate, nor on forskolin- or carbachol-induced stimulation of adenylyl cyclase. Since L-glu is released from the retina upon illumination, and receptors for this compound are present in RPE, the activation of the inositide pathway could be involved in the regulation of retina-RPE interaction, which is essential for the visual process.

Adenylyl Cyclases↗
PubMed1988

Formation of methylphosphoryl inositol phosphates by extractions that employ methanol.

Fixatives that contain methanol extract an unknown compound from several tissues including the retinas of squid (Loligo). We have determined that the compound probably contains (1) a myo-inositol ring that is phosphorylated in more than one position (including at the 5-hydroxyl), (2) a charged moiety that is not susceptible to alkaline phosphatase, and (3) a methyl group. We have found that the compound can be made by treating either phosphatidylinositol bisphosphate or human red cell ghosts with acidic methanol. We have confirmed the observation of Lips, Bross & Majerus [Proc. Natl. Acad. Sci. U.S.A. 85, 88-92] that the compound also can be made by methanolysis of inositol (cyclic 1:2,4,5)trisphosphate; however, we have not found inositol (cyclic 1:2,4,5)trisphosphate in either stimulated or unstimulated squid retinas. We tentatively identify the compound as (1-methylphosphoryl)inositol 4,5-bisphosphate formed by methanolysis of phosphatidylinositol 4,5-bisphosphate. By using this methanolysis to incorporate label from [14C]methanol, we have estimated the mass of inositol 1,4,5-trisphosphate in squid retinas to be approx. 30 mumol/l of retinal volume.

Alkaline Phosphatase↗