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D Piomelli

Publications and source records attributed to D Piomelli.

At least 73 records · Page 4Linked to original sources
PubMed1993

Arachidonic acid in cell signaling.

Important advances have recently been made in our understanding of the arachidonic acid cascade. The molecular characterization of different forms of phospholipase A2 indicates that multiple pathways are involved in the release of arachidonic acid evoked by physiological or pathological stimuli. Moreover, studies on the expression of enzymes that metabolize arachidonic acid reveal the potential participation of the eicosanoids in central aspects of cell regulation, such as control of mitogenesis. Finally, cloning of the first eicosanoid receptors is a major step towards elucidating the diverse cellular functions exerted by these bioactive lipids.

Animals↗
PubMed1993

Barium evokes glutamate release from rat brain synaptosomes by membrane depolarization: involvement of K+, Na+, and Ca2+ channels.

During K(+)-induced depolarization of isolated rat brain nerve terminals (synaptosomes), 1 mM Ba2+ could substitute for 1 mM Ca2+ in evoking the release of endogenous glutamate. In addition, Ba2+ was found to evoke glutamate release in the absence of K(+)-induced depolarization. Ba2+ (1-10 mM) depolarized synaptosomes, as measured by voltage-sensitive dye fluorescence and [3H]-tetraphenylphosphonium cation distribution. Ba2+ partially inhibited the increase in synaptosomal K+ efflux produced by depolarization, as reflected by the redistribution of radiolabeled 86Rb+. The release evoked by Ba2+ was inhibited by tetrodotoxin (TTX). Using the divalent cation indicator fura-2, cytosolic [Ca2+] increased during stimulation by approximately 200 nM, but cytosolic [Ba2+] increased by more than 1 microM. Taken together, our results indicate that Ba2+ initially depolarizes synaptosomes most likely by blocking a K+ channel, which then activates TTX-sensitive Na+ channels, causing further depolarization, and finally enters synaptosomes through voltage-sensitive Ca2+ channels to evoke neurotransmitter release directly. Though Ba(2+)-evoked glutamate release was comparable in level to that obtained with K(+)-induced depolarization in the presence of Ca2+, the apparent intrasynaptosomal level of Ba2+ required for a given amount of glutamate release was found to be several-fold higher than that required of Ca2+.

Animals↗
PubMed1993

Selection of alternative G-mediated signaling pathways at the dopamine D2 receptor by protein kinase C.

Evidence indicates that a single membrane receptor subtype may be responsible for the generation of multiple intracellular signals, but mechanisms allowing for the selection of a specific effector pathway have not yet been documented. In neurons and other cells, the stimulation of dopamine D2 receptors produces, via G-protein activation, a spectrum of intracellular responses including inhibition of adenylyl cyclase activity, modulation of K+ currents, and potentiation of Ca(2+)-evoked arachidonic acid (AA) release. In this study, we report that, in Chinese hamster ovary cells, stimulation of protein kinase C (PKC) directs the preferential coupling of transfected D2 receptors from inhibition of adenylyl cyclase to potentiation of AA release, two responses mediated by Gi. The switch between these two signaling systems is accompanied by marked changes in their GTP sensitivities, indicating that it may result from the phosphorylation of component(s) of the receptor-Gi-protein complex. Brain PKC activity is enhanced by neurotransmitters and by neuronal depolarization. Thus, the ability of this protein kinase to remodel signaling pathways at the D2 receptor may regulate these Gi-mediated responses in an activity-dependent manner, and represent a novel form of synaptic plasticity.

1-Methyl-3-isobutylxanthine↗
PubMed1992

Expression of a cloned rat histamine H2 receptor mediating inhibition of arachidonate release and activation of cAMP accumulation.

A DNA, cloned after screening a rat genomic bank with probes derived from the sequence of a putative dog histamine H2 receptor [Gantz, I., Schäffer, M., Delvalle, J., Logsdon, C., Campbell, V., Uhler, M. & Yamada, T. (1991) Proc. Natl. Acad. Sci. USA 88, 429-433], was used to prepare a probe for Northern blot analysis and to transfect Chinese hamster ovary (CHO) cells. Distribution of the gene transcripts in guinea pig tissues was consistent with that of H2 receptors. Transfected CHO cells expressed a high density of sites binding [125I]iodoaminopotentidine, a selective H2-receptor ligand. These sites were characterized as typical H2 receptors by using a series of competing agents that displayed apparent dissociation constants closely similar to corresponding values at a reference biological system. In transfected cells, histamine stimulated, with high potency and large receptor reserve, the accumulation of cAMP. In addition, in the same cells, histamine potently inhibited the release of arachidonic acid induced either by stimulation of constitutive purinergic receptors or by application of a Ca2+ ionophore. This inhibition was independent of either cAMP or Ca2+ levels. The results suggest that a single H2 receptor may be linked not only to adenylyl cyclase activation but also to reduction of phospholipase A2 activity. Because H1 receptors have been reported to stimulate arachidonic acid release, inhibition of this release, an unexpected signaling pathway for H2 receptors, may account for the opposing physiological responses elicited in many tissues by stimulation of these two receptors subtypes.

Animals↗
PubMed1992

Participation of prostaglandin E2 in dopamine D2 receptor-dependent potentiation of arachidonic acid release.

Stimulation of dopamine D2 receptors potentiates Ca2+ ionophore- or ATP-induced arachidonic acid (AA) release in D2 receptor cDNA-transfected Chinese hamster ovary (CHO) cells [CHO(D2)]. By using a combination of chromatographic, biochemical, and radioimmunochemical techniques, we show here that prostaglandin (PG) E2 is a major product of AA metabolism in CHO(D2) cells stimulated with the Ca2+ ionophore A23187. Formation of this PG was markedly increased by the concomitant application of quinpirole, a D2 receptor agonist. In addition, PGE2 enhanced D2-dependent amplification of AA release, either when it was added (EC50 = 100 nM) or when it was produced endogenously, as shown by experiments carried out with the cyclooxygenase inhibitor indomethacin. The results suggest that PGE2 may participate in D2 receptor-mediated potentiation of AA release in CHO(D2) cells. They also support a functional role for this PG in the modulation of dopaminergic transmission in areas of the CNS, such as amygdala and hypothalamus, where high levels of both PGE2 and dopamine D2 receptors are found.

Animals↗
PubMed1991

Dopamine activation of the arachidonic acid cascade as a basis for D1/D2 receptor synergism.

Understanding the actions of the neurotransmitter dopamine in the brain is important in view of its roles in neuropsychiatric illnesses. Dopamine D1 receptors, which stimulate both adenylyl cyclase and phospholipase C, and D2 receptors, which inhibit them, can nevertheless act synergistically to produce many electrophysiological and behavioral responses. Because this functional synergism can occur at the level of single neurons, another, as yet unidentified, signalling pathway activated by dopamine has been hypothesized. We report here that in Chinese hamster ovary (CHO) cells transfected with the D2 receptor complementary DNA, D2 agonists potently enhanced arachidonic acid release, provided that such release has been initiated by stimulating constitutive purinergic receptors or by increasing intracellular Ca2+. In CHO cells expressed D1 receptors, D1 agonists exert no such effect. When D1 and D2 receptors are coexpressed, however, activation of both subtypes results in a marked synergistic potentiation of arachidonic acid release. The numerous actions of arachidonic acid and its metabolites in neuronal signal transduction suggest that facilitation of its release may be implicated in dopaminergic responses, such as feedback inhibition mediated by D2 autoreceptors, and may constitute a molecular basis for D1/D2 receptor synergism.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1991

Bidirectional control of phospholipase A2 activity by Ca2+/calmodulin-dependent protein kinase II, cAMP-dependent protein kinase, and casein kinase II.

In preparations of synaptic terminals (synaptosomes) isolated from rat brain, the activity of phospholipase A2 (PLA2), a phospholipid hydrolase that serves a central function in signal transduction, was inhibited in a Ca(2+)-dependent manner by incubation with 60 mM K+ or with the Ca(2+)-selective ionophore ionomycin. Reversal by alkaline phosphatase treatment suggested that this inhibitory effect resulted from phosphorylation of a synaptosomal protein substrate. When lysed synaptosomes were incubated with Ca2+/calmodulin (CaM), purified Ca2+/CAM-dependent protein kinase II (Ca2+/CaM-dependent PK II) and ATP, PLA2 activity in lysates was nearly abolished within 10 min. This effect was accompanied by a marked decrease in the Vmax of the enzyme and little or no change in the Km. Furthermore, Ca2+/CaM with ATP but without exogenous Ca2+/CaM-dependent PK II partially inhibited PLA2 activity, and this effect was prevented by treating the lysates with a selective peptide inhibitor of Ca2+/CaM-dependent PK II. In contrast, incubation of intact synaptosomes with 4 beta-phorbol 12-myristate 13-acetate or of lysed synaptosomes with purified protein kinase C had little or no effect on PLA2 activity. The results strongly suggest that the Ca(2+)-dependent inhibition of PLA2 activity observed in intact nerve endings was produced by activation of the multifunctional Ca2+/CaM-dependent PK II. A membrane-permeable adenylyl cyclase activator, forskolin, enhanced PLA2 activity in intact synaptosomes, and cAMP-dependent protein kinase potentiated PLA2 activity in lysed synaptosomes. Furthermore, another broad-spectrum protein kinase present in synaptic terminals, casein kinase II, also potentiated PLA2 activity in lysed synaptosomes. The effects of both protein kinases were associated with a decrease in Km and no change in Vmax. The results suggest that PLA2 activity in synaptic terminals is subject to bidirectional control by distinct signal transduction pathways. Moreover, mutually antagonistic effects of the Ca2+/CaM-dependent PK II and PLA2 pathways provide a possible molecular mechanism for bidirectional modulation of neurotransmitter release.

Animals↗
PubMed1991

A phospholipase A2-stimulating protein regulated by protein kinase C in Aplysia neurons.

We describe some properties on an Mr 30,000 thermolabile and trypsin-sensitive protein that activates phospholipase A2 (PLA2) and which was isolated from nervous tissue of the marine mollusk, Aplysia californica. A similar protein is present in rat cerebral cortex. This protein was partially purified from crude homogenates of nervous tissue by ion exchange chromatography on DEAE-Sephadex followed by size-exclusion high performance liquid chromatography (HPLC). It is loosely associated with membrane fractions, and is extracted by 0.05% Tween 20. Although similar in size to several previously described PLA2-stimulating proteins from non-neural mammalian cells and tissues, it differs from them in some aspects of biological activity. The protein promotes the release of eicosanoids from the membranes of intact Aplysia neurons prelabeled with [3H]arachidonic acid and appears to be an in vitro substrate for protein kinase C (PKC). PLA2-stimulating activity is greatly enhanced after exposing isolated ganglia to phorbol dibutyrate (PDBu) and is reduced by treatment with immobilized E. coli alkaline phosphatase. These observations suggest that phosphorylation of this stimulatory protein by PKC regulates PLA2 in neurons.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1991

Metabolism of arachidonic acid in nervous system of marine mollusk Aplysia californica.

Studies of the marine mollusk Aplysia californica indicate that products of the 12-lipoxygenase pathway may be involved in neuronal intracellular signaling. The nervous tissue of Aplysia has a 12-lipoxygenase activity that converts both exogenous and endogenous arachidonic acid to an array of products, which include 12-hydroperoxyeicosatetraenoic acid (12-HPETE) and its metabolites hepoxilin A3, hepoxilin B3, 12-ketoeicosatetraenoic acid, and 12-oxododecatrienoic acid. These eicosanoids were identified using a combination of high-performance liquid chromatography, ultraviolet spectrometry and gas chromatography-mass spectrometry. Generation of 12-lipoxygenase products was stimulated by application of the neurotransmitters, histamine and FMRF-amide, or by stimulation of identified neural cells. In electrophysiological studies of identified L14 and sensory neurons it was found that 12-HPETE and its metabolic products exert physiological actions that resemble those of histamine and FMRF-amide. These results suggest that products of 12-HPETE metabolism may act as second messengers in Aplysia neurons.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1990

Lipoxygenase metabolites of arachidonic acid in neuronal transmembrane signalling.

Studies of invertebrate and vertebrate nervous tissue have demonstrated that free arachidonic acid and its lipoxygenase metabolites are produced in a receptor-dependent fashion. The intracellular actions of these compounds include the regulation of activity of membrane ion channels and protein kinases. In this article Daniele Piomelli and Paul Greengard review the evidence that these lipophilic molecules constitute a novel class of intracellular second messenger, possibly involved in the modulation of neurotransmitter release.

Animals↗
PubMed1989

Inhibition of Ca2+/calmodulin-dependent protein kinase II by arachidonic acid and its metabolites.

A variety of evidence indicates that activation of Ca2+/calmodulin-dependent protein kinase II (CaM-kinase II) in nerve terminals leads to enhanced neurotransmitter release. Arachidonic acid and its 12-lipoxygenase metabolite, 12-hydroperoxyeicosatetraenoic acid (12-HPETE), have been suggested to act as second messengers mediating presynaptic inhibition of neurotransmitter release. In the present study it was found that CaM-kinase II, purified from rat brain cortex, was inhibited both by arachidonic acid (IC50 = 24 microM) and by 12-HPETE (IC50 = 0.7 microM). Neither substance inhibited CaM-kinase I or III, protein kinase C, or the catalytic subunit of cAMP-dependent protein kinase. Specific inhibition of Ca2+/calmodulin-dependent protein phosphorylation by arachidonic acid was also demonstrated in intact synaptic terminals (synaptosomes) isolated from rat forebrain. These results suggest that arachidonate and its metabolites may modulate synaptic function through the inhibition of CaM-kinase II-dependent protein phosphorylation.

Amino Acid Sequence↗
PubMed1989

Formation and action of 8-hydroxy-11,12-epoxy-5,9,14-icosatrienoic acid in Aplysia: a possible second messenger in neurons.

In Aplysia neural tissue, the release and metabolism of arachidonic acid are stimulated by histamine or by activation of the identified L32 nerve cell circuit of the abdominal ganglion. Previously we found that histamine and intracellular stimulation of L32 cells, which are putatively histaminergic neurons, cause the production of 12-hydroxy-5,8,10,14-icosatetraenoic acid (12-HETE), a product of the 12-lipoxygenase pathway formed through 12-hydroperoxy-5,8,10,14-icosatetraenoic acid (12-HPETE). 12-HPETE, but not 12(S)-HETE, mimics the dual-action response of L14 ink motor neurons to histamine and stimulation of L32. 12-HPETE can also be further metabolized to 8-hydroxy-11,12-epoxy-5,9,14-icosatrienoic acid (8-HEpETE) which was identified by HPLC, enzymatic hydrolysis, and GC/MS. Production of 8-HEpETE is specific, as its positional isomer 10-hydroxy-11,12-epoxy-5,8,14-icosatrienoic acid is not formed after physiologic stimulation. 8-HEpETE can elicit the late component (hyperpolarization) of the dual-action response in L14 cells, suggesting that it may be a second messenger in Aplysia.

8,11,14-Eicosatrienoic Acid↗
PubMed1989

12-keto-eicosatetraenoic acid. A biologically active eicosanoid in the nervous system of Aplysia.

The lipoxygenase product 12-hydroperoxy-5,8,10,14-eicosatetraenoic acid (12-HPETE), stimulates the synaptic response produced by the modulatory transmitter histamine and the neuroactive peptide Phe-Met-Arg-Phe-amide (FMRFamide) in identified neurons of the marine mollusk Aplysia californica. The 12-lipoxygenase pathway has not yet been fully characterized, but 12-HPETE is known to be metabolized further. Therefore, we began to search for other metabolites in order to investigate whether the actions of 12-HPETE might require its conversion to other active products. We have identified 12-keto-5,8,10,14-eicosatetraenoic acid (12-KETE) as a metabolite of 12-HPETE formed by Aplysia nervous tissue. 12-KETE was identified in incubations of the tissue with arachidonic acid using HPLC, UV spectrometry, and gas-chromatography/mass spectrometry. [3H]12-KETE is formed from endogenous lipid stores in nervous tissue, labeled with [3H]arachidonic acid upon stimulation by application of histamine. In L14 and L10 cells, identified neurons in the abdominal ganglion, applications of 12-KETE elicit changes in membrane potential similar to those evoked by histamine. Another metabolite of 12-HPETE, 12(s)-hydroxy-5,8,10,14-eicosatetraenoic acid [12(S)-HETE], is inactive. These results support the hypothesis that 12-HPETE and its metabolite, 12-KETE, participate in transduction of histamine responses in Aplysia neurons.

Animals↗
PubMed1988

Formation and biological activity of 12-ketoeicosatetraenoic acid in the nervous system of Aplysia.

12-Hydroperoxy-5,8,10,14-eicosatetraenoic acid (12-HPETE), a lipoxygenase product, simulates the synaptic responses produced by the modulatory transmitter, histamine, and the neuroactive peptide, Phe-Met-Arg-Phe-amide (FMRFamide), in identified neurons of the marine mollusk, Aplysia californica (Piomelli, D., Shapiro, E., Feinmark, S. J., and Schwartz, J. H. (1987) J. Neurosci. 7, 3675-3886; Shapiro, E., Piomelli, D., Feinmark, S., Vogel, S., Chin, G., and Schwartz, J. H. (1988) Cold Spring Harbor Symp. Quant. Biol. 53, in press). The 12-lipoxygenase pathway has not yet been fully characterized, but 12-HPETE is known to be metabolized further. We therefore began to search for other metabolites in order to investigate whether the actions of 12-HPETE might require its conversion to other active products. Here we report the identification of 12-keto-5,8,10,14-eicosatetraenoic acid (12-KETE), a metabolite of 12-HPETE formed by Aplysia nervous tissue. This product was identified in incubations of the tissue with arachidonic acid using high performance liquid chromatography, UV spectrometry, and gas chromatography/mass spectrometry. [3H]12-KETE was formed from endogenous lipid stores in nervous tissue, labeled by incubation with [3H]arachidonic acid, when stimulated by application of histamine. In L14 and L10 cells, identified neurons in the abdominal ganglion, applications of 12-KETE elicit changes in membrane potential similar to those evoked by histamine. 12(S)-Hydroxy-5,8,10,14-eicosatetraenoic acid, another metabolite of 12-HPETE, is inactive. These results support the hypothesis that 12-HPETE and its metabolite, 12-KETE, participate in transduction of histamine responses in Aplysia neurons.

Animals↗
PubMed1987

Antagonistic actions of prostaglandins E2 and F2 alpha on the isolated lungs of the frog, Rana esculenta L.

Isolated lungs of the frog, Rana esculenta L., when incubated in amphibian Ringer solution for 30 min, produced a prostaglandin E2-like substance (27.1 +/- 3.8 ng/g w.w.), as determined by bioassay on the isolated rat stomach strip. The release of PGE2-like substance from skin, heart and bowel is also reported. The activity of synthetic prostaglandins E2 (PGE2) and F2 alpha (PGF2 alpha) on the muscular contractility of frog isolated lungs was investigated: PGE2 and PGF2 alpha relaxed and contracted respectively in a dose-dependent manner this preparation, a result similar to that obtained in mammals.

Animals↗