SEARCH · PubMed Health

Results for “PHOSPHOINOSITIDES”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 739 records · Page 41Linked to original sources

PubMed1988

Effects of acetylcholine and other agents on 32P-prelabeled phosphoinositides and phosphatidate in crude synaptosomal preparations.

Experimental conditions are described which permit effects of various agents on polyphosphoinositides and phosphatidic acid (PA) to be evaluated simultaneously in crude nerve-ending preparations from rat brain. Acetylcholine (3-100 microM) or carbachol (30-1,000 microM) induced the hydrolysis of prelabeled polyphosphoinositides and, at the same time, stimulated the net label incorporated in phosphatidic acid. All muscarinic effects were blocked by atropine or pirenzepine. Non-muscarinic agonists (glutamate, adenosine, norepinephrine) stimulated polyphosphoinositide hydrolysis in this preparation, but of these only norepinephrine affected phosphatidic acid turnover. A potentiation of acetylcholine-induced phosphoinositide turnover by KCl was observed, as well as an apparent selective inhibition of PIP2 hydrolysis by LiCl. Acetylcholine-stimulated turnover of PA was not necessarily coupled to phosphoinositide hydrolysis.

Acetylcholine↗

PubMed2003

Analysis of class I phosphoinositide 3-kinase autophosphorylation sites by mass spectrometry.

This article describes the identification of the autophosphorylation sites of the G protein-sensitive class I phosphoinositide 3-kinase isoforms beta and gamma by mass spectrometry. Since discrimination and suppression effects prevented the immediate detection and sequencing of phosphopeptides in complex mixtures, a strategy was applied that involved (32)P-radiolabeling of the phosphoproteins, cleavage of the phosphoproteins with several proteases and/or cyanogen bromide, separation of the resulting peptide mixtures by micro-reversed-phase liquid chromatography, and mass spectrometric analysis of fractions containing phosphopeptides. As a result the primary autophosphorylation sites of phosphoinositide 3-kinase p110beta and p110gamma subunits could be unambiguously assigned to the C-terminal Ser 1070 and Ser 1101, respectively.

Amino Acid Sequence↗

PubMed1993

Endogenous phosphoinositide precursors of inositol phosphates in rat brain cortical membranes.

The appearance of Ins1P as an index of direct PtdIns breakdown by phospholipase C was examined in rat brain cortical membranes using either exogenous [3H]PtdIns substrate or [3H]inositol-prelabeled endogenous phosphoinositide substrates. Production of [3H]Ins1P was observed using exogenous [3H]PtdIns but not with endogenous substrate over the physiological range of calcium concentrations. [3H]Ins1,4P2 and [3H]Ins4P, derived from phospholipase C breakdown of polyphosphoinositides, were formed by membranes from both exogenous [3H]PtdIns and endogenous 3H-phosphoinositides, in the presence of ATP. The contribution of endogenous PtdInsP2 and PtdInsP to the generation of inositol phosphates was examined in membranes from [3H]inositol-prelabeled brain slices by adding unlabeled Ins1,4,5P3 to trap [3H]Ins1,4,5P3 generated upon breakdown of [3H]PtdInsP2. The maximal rate of [3H]Ins1,4,5P3 appearance was attained in the presence of 150-200 microM added Ins1,4,5P3 and represented 12.5% of the combined rates of formation of [3H]Ins1,4,5P3 and [3H]Ins1,4P2, similar to the content of [3H]PtdInsP2 relative to total 3H-polyphosphoinositides. The results show that, while endogenous PtdIns is not degraded by phospholipase C, the enzyme appears to be equally effective to cleave endogenous PtdInsP2 and PtdInsP.

Animals↗

PubMed1993

Neomycin and spermine have similar effects on secretion and phosphoinositide metabolism in ATP-depleted permeabilized adrenal chromaffin cells.

To evaluate the requirement of bovine adrenal chromaffin cells for inositol phospholipids in secretion, the effects of neomycin and spermine on secretion and phosphoinositide metabolism were compared. Spermine and neomycin had virtually identical effects on secretion and phosphoinositide levels. Both polyamines 1) partially maintained secretion when added to permeabilized cells in the absence of ATP, 2) had no effect when added to cells in the presence of ATP and 3) inhibited secretion when present with the Ca2+ stimulus. In the absence of ATP the enhancements to secretion due to incubation with either polyamine were associated with sustained levels of the polyphosphoinositides. The ability of spermine and neomycin to maintain secretion and the polyphosphoinositides in the absence of ATP supports the hypothesis that the maintenance of the polyphosphoinositides is necessary for secretion. Neomycin was found to inhibit Ca2+ stimulated production of both inositol bis- and tris-phosphates while spermine was found to selectively inhibit inositol bis-phosphate production and had no effect on Ca(2+)-stimulated inositol tris-phosphate production in permeabilized cells.

Adenosine Triphosphate↗

PubMed1999

Mouse phosphoinositide 3-kinase p110alpha gene: cloning, structural organization, and localization to chromosome 3 band B.

Phosphoinositide 3-Kinases (PI3-Kinases) are a family of dual specificity enzymes with a unique lipid kinase activity toward the D-3 position of the inositol ring of phosphoinositides and a less well characterized serine/threonine protein kinase activity. Class IA PI3-Kinases comprise a 110-120 kDa catalytic subunit (usually termed p110) and an 85 kDa or 50 to 55 kDa regulatory subunit (often called p85). cDNAs for three mammalian Class IA PI3-Kinase catalytic subunits designated p110alpha, p110beta, and p110delta have been cloned from several species. A YAC clone for the human p110alpha gene has also been cloned and mapped to chromosome 3q26.3. However, structural organization for any of the PI3-Kinase p110alpha genes has not been reported. Here, we report the cloning, structural organization, and chromosomal localization of the mouse PI3-Kinase p110alpha gene. The translated portion of the mouse p110alpha gene is encoded by 19 exons that span at least 24 kb. Dual color fluorescence in situ hybridization (FISH) was performed to determine the chromosomal localization of the mouse PI3-Kinase p110alpha gene. FISH results and DAPI banding demonstrated localization of the p110alpha gene to band B on mouse chromosome 3, a region syntenic with human chromosome 3q26.3.

Animals↗

PubMed1994

Comparison of PDGF-AA- and PDGF-BB-induced phosphoinositide formation in human and mouse fibroblasts.

In certain cells, such as human fibroblasts (AG 1523), there is a clear difference in the cell motility response induced by the different isoforms of platelet-derived growth factor (PDGF). PDGF-BB induces extensive actin reorganization and is a potent chemotactic agent, whereas PDGF-AA has a limited effect on actin reorganization and is not chemotactic. In the present study, we wanted to compare these effects on cell motility with the effects of the PDGF isoforms on phosphoinositide (PtdIns) turnover. We find that stimulation of serum-starved AG 1523 cells with PDGF-AA or PDGF-BB caused an initial increase of the phosphatidylinositol phosphate and bisphosphate (PtdInsP and PtdInsP2) pools, suggesting that activation of the phosphoinositide kinases is an initial response to PDGF stimulation. Despite a lower number of PDGF alpha-receptors than beta-receptors on these cells, the initial formation of PtdInsP and PtdInsP2 appears to be stimulated to a similar degree by the two PDGF isoforms. In contrast, PtdInsP2 hydrolysis, indirectly measured as formation of phosphatidic acid, was correlated to the number of receptors. During prolonged exposure to PDGF-BB the stimulated PtdIns turnover remained at a high level, whereas the effect of PDGF-AA appeared more transient. A marked increase in the synthesis of a component migrating as phosphatidylinositol trisphosphate (PtdInsP3) was also detected after stimulation with PDGF-BB for 5 min. With PDGF-AA minor amounts were found, indicating that activation of the PtdIns 3'-kinase occurs also via the PDGF alpha-receptor. Stimulation with PDGF-BB, but not -AA, also induced a 50% decrease in lyso-PtdIns. In murine fibroblasts (Swiss 3T3), where the two PDGF isoforms have a similar effect on cell motility, the two PDGF isoforms also similarly induced PtdIns turnover, PtdInsP3 formation, and a decrease in lyso-PtdIns. Thus, there seems to be a correlation between PDGF-induced PtdIns turnover and PDGF-induced actin reorganization. This is compatible with previous evidence suggesting the microfilament formation is directly linked to an increased turnover of polyphosphoinositides in stimulated cells.

3T3 Cells↗

PubMed1998

Structural and mechanistic comparison of prokaryotic and eukaryotic phosphoinositide-specific phospholipases C.

Phosphoinositide-specific phospholipases C (PI-PLCs) are ubiquitous enzymes that catalyse the hydrolysis of phosphoinositides to inositol phosphates and diacylglycerol (DAG). Whereas the eukaryotic PI-PLCs play a central role in most signal transduction cascades by producing two second messengers, inositol-1,4,5-trisphosphate and DAG, prokaryotic PI-PLCs are of interest because they act as virulence factors in some pathogenic bacteria. Bacterial PI-PLCs consist of a single domain of 30 to 35 kDa, while the much larger eukaryotic enzymes (85 to 150 kDa) are organized in several distinct domains. The catalytic domain of eukaryotic PI-PLCs is assembled from two highly conserved polypeptide stretches, called regions X and Y, that are separated by a divergent linker sequence. There is only marginal sequence similarity between the catalytic domain of eukaryotic and prokaryotic PI-PLCs. Recently the crystal structures of a bacterial and a eukaryotic PI-PLC have been determined, both in complexes with substrate analogues thus enabling a comparison of these enzymes in structural and mechanistic terms. Eukaryotic and prokaryotic PI-PLCs contain a distorted (beta alpha)8-barrel as a structural motif with a surprisingly large structural similarity for the first half of the (beta alpha)8-barrel and a much weaker similarity for the second half. The higher degree of structure conservation in the first half of the barrel correlates with the presence of all catalytic residues, in particular two catalytic histidine residues, in this portion of the enzyme. The second half contributes mainly to the features of the substrate binding pocket that result in the distinct substrate preferences exhibited by the prokaryotic and eukaryotic enzymes. A striking difference between the enzymes is the utilization of a catalytic calcium ion that electrostatically stabilizes the transition state in eukaryotic enzymes, whereas this role is filled by an analogously positioned arginine in bacterial PI-PLCs. The catalytic domains of all PI-PLCs may share not only a common fold but also a similar catalytic mechanism utilizing general base/acid catalysis. The conservation of the topology and parts of the active site suggests a divergent evolution from a common ancestral protein.

Amino Acid Sequence↗

PubMed2001

The effects of deimination of myelin basic protein on structures formed by its interaction with phosphoinositide-containing lipid monolayers.

The recombinant 18.5-kDa charge isoform of murine myelin basic protein (rmMBP) is unmodified posttranslationally and was used to study the effects of deimination, i.e., the conversion of arginyl to citrullinyl residues, on the protein's interactions with itself and with lipids. The unmodified species rmMBP-Cit(0) (i.e., containing no citrullinyl residues) interacted with binary monolayers containing acidic (phosphatidylinositol) and nickel-chelating lipids to form paracrystalline arrays with 4.8-nm spacing. A sample of protein was deiminated to an average of 9 citrullinyl residues per molecule of protein, yielding rmMBP-Cit(9). Under both low- and high-salt conditions, this species formed better-ordered domains than rmMBP-Cit(0), viz., planar crystalline assemblies. Thus, deimination of MBP resulted in a significant alteration of its lipid-organizing and self-interaction properties that might be operative in myelin in vivo, especially in progression of the autoimmune disease multiple sclerosis. Comparisons of amino acid sequences indicated significant similarities of MBP with filaggrin, a protein that is deiminated in another autoimmune disease, rheumatoid arthritis, suggesting that comparable epitopes could be targeted in both pathologies. In contrast, binary lipid monolayers consisting of phosphatidylinositol-4-phosphate (or phosphatidylinositol-4,5-bisphosphate) and a nickel-chelating lipid formed helical tubular vesicular structures, which appeared to be induced and/or stabilized by rmMBP, especially in its deiminated form. Sequence comparisons with other actin- and phosphoinositide-binding proteins (vinculin, ActA, MARCKS) suggested that the carboxyl-terminal segment of MBP could form an amphipathic alpha helix and was the phosphoinositide binding site.

Amino Acid Sequence↗

PubMed1991

Potent inhibitory action of chlorethylclonidine on the positive inotropic effect and phosphoinositide hydrolysis mediated via myocardial alpha 1-adrenoceptors in the rabbit ventricular myocardium.

The influence of the alpha 1b-adrenoceptor-selective antagonist chlorethylclonidine on the alpha 1-adrenergic positive inotropic effect and the phosphoinositide hydrolysis induced by phenylephrine was investigated in the rabbit ventricular myocardium. Pretreatment of membrane fractions derived from the rabbit ventricular muscle with 10(-5) mol/l chlorethylclonidine decreased the specific binding of [3H]prazosin (at a saturating concentration of 10(-9) mol/l) from the control value of 11.27 +/- 0.48 to 4.18 +/- 1.87 fmol/mg protein. The inhibition by adrenaline of the binding of [3H]prazosin (slope factor and affinity) was not affected by chlorethylclonidine. The positive inotropic effect of phenylephrine (in the presence of 3 x 10(-7) mol/l bupranolol) was inhibited by chlorethylclonidine in a concentration-dependent manner (10(-7)-10(-5) mol/l) and abolished by 10(-5) mol/l chlorethylclonidine. The concentration of chlorethylclonidine to inhibit the phenylephrine-induced maximum response to 50% was 2.4 x 10(-6) mol/l. The accumulation of [3H]inositol monophosphate and [3H]inositol trisphosphate induced by 10(-5) mol/l phenylephrine was inhibited by chlorethylclonidine in the same concentration range. These findings indicate that the myocardial alpha 1-adrenoceptors mediating a positive inotropic effect in the rabbit ventricular myocardium may belong to the chlorethylclonidine-sensitive alpha 1b-subtype, and that the subcellular mechanism of action involve phosphoinositide hydrolysis.

Adrenergic alpha-Antagonists↗

PubMed1990

Growth hormone increases phosphoinositide turnover in rat adipocytes that are sensitive to the insulin-like action of the hormone.

UNLABELLED: The effect of pituitary human growth hormone (hGH) on the 32P-labelling of phosphoinositides and phosphatidic acid was studied in noradrenaline-stimulated rat adipocytes which were either responsive or non-responsive to the antilipolytic (insulin-like) effect of hGH. In cells responsive to the insulin-like effect of hGH, hormone treatment resulted in a marked increase of the 32P-labelling of phosphatidic acid and phosphatidyl inositol in the plasma membrane, high density microsomal, and low density microsomal fractions. The increased 32P-labelling most likely reflects an activation of phosphoinositide phospholipase C. ABBREVIATIONS: IP3 - Myo-Inositol 1,4,5-Triphosphate. BSA - Bovine Serum Albumin, HEPES - N-2-Hydroxyethylpiperazine-N'-2-Ethanesulphonic Acid, hGH - Human Pituitary Growth Hormone, LPC-Lysophosphatidylcholine, LPE - Lysophosphatidylethanolamine, LPI - Lysophosphatidylinositol, PA - Phosphatidic Acid, PC - Phosphatidylcholine, PE - Phosphatidylethanolamine, PI - Phosphatidylinositol, PIP - Phosphatidylinositol-4-Phosphate, PIP2-Phosphatidylinositol-4,5-Diphosphate, PS-Phosphatidylserine.

Adipose Tissue↗

PubMed1988

Time-dependent potentiation of insulin release induced by alpha-ketoisocaproate and leucine in rats: possible involvement of phosphoinositide hydrolysis.

The ability of the amino acid leucine and its keto acid, alpha-ketoisocaproate, to induce insulin release, to initiate phosphoinositide hydrolysis, and to amplify the subsequent insulin secretory response to glucose was assessed. In islets whose inositol-containing lipids were prelabelled with myo[2-3H]inositol, the addition of either compound resulted in an increase in insulin output, an increase in 3H efflux, rapid and significant increases in labelled inositol phosphate accumulation and a sustained increase in 3H efflux after removal of the stimulant. Direct measurements of labelled inositol phosphate accumulation in islets previously stimulated with alpha-ketoisocaproate demonstrate that this sustained increase in 3H efflux was the result of a persistent increase in phosphoinositide hydrolysis and was not simply a consequence of the hydrolysis of preformed inositol phosphates into more membrane permeable species. Prior exposure of islets to alpha-ketoisocaproate or leucine also resulted in an amplified secretory response to a subsequent glucose (10 mmol/l) stimulus. While peak first phase insulin release averaged 66 +/- 4 (mean +/- SEM, n = 18) pg.islet-1. min-1 from control islets, this value increased to 204 +/- 14 and 246 +/- 11 pg.islet-1.min-1 in the leucine or alpha-keto-isocaproate pretreated islets respectively. The duration of this amplified response paralleled the duration of the persistent increase in 3H efflux. Prior alpha-ketoisocaproate exposure also amplified the subsequent insulin secretory response to tolbutamide and glyceraldehyde.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Aluminium impacts elements of the phosphoinositide signalling pathway in neuroblastoma cells.

Inositol phosphate formation was examined in aluminium-treated murine neuroblastoma cells labelled with [3H]-myoinositol. Employing fluoride-stimulated intact cells, aluminium (0.2 microM to 1 mM) reduced inositol phosphate formation in a dose-dependent manner. In digitonin-permeabilized cells, stimulated with nonhydrolyzable GTP[S], inositol phosphate formation was also inhibited by increasing aluminium doses; the IC50 value was about 20 microM aluminium, while the inositol phosphate level was reduced 2.5 to 3 fold by 50 microM aluminium. The inhibitory effect of aluminium (50 microM) could not be reversed by increasing GTP[S] concentrations up to 500 microM. Prechelation of aluminium to citrate or EGTA completely abolished the aluminium-triggered inhibition of fluoride-stimulated inositol phosphate formation in intact cells, but had little effect on the inhibition of permeabilized cells stimulated with GTP[S]. In neuroblastoma cells phosphoinositide hydrolysis could be evoked either through a pathway involving the Mg2+/guanine nucleotide binding (Gp) protein, or via a pathway operative in the presence of high intracellular Ca2+ concentrations. In the Mg2+/Gp protein-mediated pathway, formation of inositol triphosphate, IP3, inositol diphosphate, IP2, and inositol monophosphate, IP, was apparently inhibited by aluminium in an interdependent manner. As to the Ca(2+)-mediated pathway, aluminium application mainly diminished the release of IP3. Following interiorization, aluminium thus acts upon elements critical for phosphoinositide-associated signal transduction. An aluminium target apparently resides on the Gp protein. Phosphatidylinositol-4,5-diphosphate-specific phospholipase C probably harbours a second aluminium target.

Aluminum↗

PubMed1992

Cholinergic hyperinnervation in the cerebral cortex of microencephalic rats does not result in muscarinic receptor down-regulation or in alteration of receptor-stimulated phosphoinositide metabolism.

Administration of methylazoxymethanol (MAM; 25 mg/kg) to pregnant rats at gestational day 15 (GD 15) induces a marked reduction of telencephalic areas of the offspring brain. Previous neurochemical studies demonstrated a marked cholinergic hyperinnervation in the cerebral cortex of microencephalic rats. In this study we have evaluated whether this cholinergic hyperinnervation could result in altered functionality of muscarinic receptors. Acetylcholinesterase activity (AChE) was increased by 69% in the cerebral cortex of MAM treated rats, confirming a relative hyperinnervation, whereas in the hippocampus and striatum no significant changes were observed. Despite the marked hyperinnervation, in the cerebral cortex of microencephalic rats neither muscarinic receptor-stimulated phosphoinositide metabolism nor muscarinic receptor density were altered. No differences in receptor density were also observed in the hippocampus and striatum. Chronic diisopropylfluorophosphate (DFP) administration induced a marked decrease of AChE activity and down-regulation of muscarinic receptors whereas atropine administration resulted in receptor up-regulation in cerebral cortex, striatum and hippocampus of both control and MAM rats. The results confirm a relative cholinergic hyperinnervation in the cerebral cortex of microencephalic rats and demonstrate that the regulation of muscarinic receptor-stimulated phosphoinositide metabolism and muscarinic receptor plasticity is not modified in a condition of increased cholinergic presynaptic terminals.

Abnormalities, Drug-Induced↗

PubMed1990

Potassium ions potentiate the muscarinic receptor-stimulated phosphoinositide metabolism in cerebral cortex slices: a comparison of neonatal and adult rats.

Activation of cholinergic muscarinic receptors results in an increased turnover of membrane inositol phospholipids. In rat cerebral cortex slices, carbachol- and acetylcholine-induced inositol phosphates ([3H]InsPs) accumulation is maximal in 7 day-old rats and lowest in adults, while the density of muscarinic binding sites increases gradually with age, suggesting the presence of a more effective receptor-effector coupling during neonatal life. In the process of investigating the nature of such differential stimulation, we have studied the effects of potassium ions on muscarinic receptor-stimulated phosphoinositide metabolism during development. Increasing the concentration of K+ from 6 to 12 mM potentiated the stimulating effect of carbachol by 80-100% in adult animals, as previously shown, but only 10-20% in 7 day-old animals, without altering its EC50 values. The differential potentiation by K+ at these two ages was specific for muscarinic receptors, since norepinephrine-stimulated accumulation was potentiated only 18% and 12% in adult and 7 day-old rats, respectively. Two other monovalent cations, rubidium and cesium, had the same effect as K+ on carbachol-stimulated [3H]-InsPs accumulation. The effect of K+ was not antagonized by the K+ channel blocker 4-aminopyridine, but was antagonized by tetraethylammonium (TEA). TEA, however, also interacted with muscarinic binding sites. Omission of calcium from the incubation medium did not influence the potentiating effect of K+ during development was inversely proportional to the stimulation of phosphoinositide metabolism induced by carbachol. These results suggest that the mechanism responsible for the potentiating effect of K+ in adult rats might be already operating in neonatal animals.

Aging↗

PubMed1990

Regulation by batrachotoxin, veratridine, and monensin of basal and carbachol-induced phosphoinositide hydrolysis in neurohybrid NCB-20 cells.

Batrachotoxin (BTX), veratridine and monensin induced a time- and dose-dependent increase of [3H]-inositol monophosphate (3H-IP1) accumulation in the presence of lithium in prelabeled neurohybrid NCB-20 cells. A decrease of NaCl concentration to less than 30 mM markedly increased basal 3H-IP1 accumulation; however, the percentage of stimulation induced by these three agents remained unchanged even in the complete absence of sodium. The stimulation of phosphoinositide hydrolysis induced by these agents was detected in the absence of lithium but was largely prevented in the calcium-free medium. Tetradotoxin (TTX) blocked effects of BTX and veratridine (IC50 approximately 20nM), but not that stimulated by monensin. Thus, calcium-dependent activation of phospholipase C by these agents did not involve the entry of sodium or lithium. BTX and monensin also induced greater than additive effects on carbachol-induced 3H-IP1 accumulation. These effects were also TTX-sensitive and involved an increase in the Vmax and a decrease in the EC50 for carbachol. Veratridine provoked strikingly different effects on carbachol-dependent phosphoinositide turnover, depending on the passage number of the cells.

Batrachotoxins↗

PubMed1989

Microwave induced stimulation of 32Pi incorporation into phosphoinositides of rat brain synaptosomes.

Exposure of synaptosomes to microwave radiation at a power density of 10 mW/sq cm or more produced stimulation of the 32Pi-incorporation into phosphoinositides. The extent of 32Pi incorporation was found to be much more pronounced in phosphatidylinositol-4-phosphate (PIP), and phosphatidylinositol-4,5-bisphosphate (PIP2) as compared to phosphatidylinositol (PI) and phosphatidic acid (PA). Other lipids were also found to incorporate 32Pi but no significant changes in their labeling were seen after exposure to microwave radiation. Inclusion of 10 mM lithium in the medium reduced the basal labeling of PIP2, PIP and PI and increased PA labeling. Li+ also inhibited the microwave stimulated PIP2, PIP and PI labeling but had no effect on PA labeling. Calcium ionophore, A23187, inhibited the basal and microwave stimulated 32Pi labeling of PIP and PIP2, stimulated basal labeling of PA and PI and had no effect on microwave stimulated PA and PI labeling. Calcium chelator, EGTA, on the other hand, had no effect on basal labeling of PA and PI, stimulated basal PIP and PIP2 labeling but did not alter microwave stimulated labeling of these lipids. Exposure of synaptosomes to microwave radiation did not alter the chemical concentration of phosphoinositides indicating that the turnover of these lipids was altered. These results suggest that low frequency microwave radiation alter the metabolism of inositol phospholipids by enhancing their turnover and thus may affect the transmembrane signalling in the nerve endings.

Animals↗

PubMed1992

Phospholipids in Trypanosoma cruzi: phosphoinositide composition and turnover.

The polyphosphoinositides from Trypanosoma cruzi were isolated by preparative thin-layer chromatography (TLC) and identified. When myo-[3H]inositol was present in the culture medium for five days, analyses showed the presence of phosphatidylinositol (PI), lysophosphatidylinositol (lysoPI), phosphatidylinositol 4-phosphate (PIP) and phosphatidylinositol 4,5-bisphosphate (PIP2). Short-term incubation with 32Pi led to higher percentages of incorporation into phosphatidylethanolamine (PE), lysophosphatidylethanolamine (lysoPE) and PI compared to the other glycerophospholipids. The phosphoinositides (PI, PIP and PIP2) contained a larger proportion of unsaturated than saturated fatty acids. High proportions of 18:2 were found in the three phosphoinositides analyzed, whereas the major saturated fatty acid was 18:0. Water-soluble inositol phosphates (IP, IP2 and IP3) were also identified.

Animals↗

PubMedDate not supplied

Axon-myelin transfer of phospholipids and phospholipid precursors. Labeling of myelin phosphoinositides through axonal transport.

Previous studies have provided evidence for axon-to-myelin transfer of intact lipids and lipid precursors for reutilization by myelin enzymes. Several of the lipid constituents of myelin showed significant contralateral/ipsilateral ratios of incorporated radioactivity, indicative of axonal origin, whereas proteins and certain other lipids did not participate in this transfer-reutilization process. The present study will examine the labeling of myelin phosphoinositides by this pathway. Both 32PO4 and [3H]inositol were injected monocularly into 7-9-wk-old rabbits and myelin was isolated 7 or 21 days later from pooled optic tracts and superior colliculi. In total lipids 32P counts of the isolated myelin samples showed significant contralateral/ipsilateral ratios as well as increasing magnitude of contralateral-ipsilateral differences during the time interval. Thin-layer chromatographic isolation of the myelin phosphoinositides revealed significant 32P-labeling of these species, with PIP and PIP2 showing time-related increases. This resembled the labeling pattern of the major phospholipids from rabbit optic system myelin in a previous study and suggested incorporation of axon-derived phosphate by myelin-associated enzymes. The 32P label in PI, on the other hand, remained constant between 7 and 21 days, suggesting transfer of intact lipid. This was supported by the labeling pattern with [3H]inositol, which also showed no increase over time for PI. These results suggest axon-myelin transfer of intact PI followed by myelin-localized incorporation of axon-derived phosphate groups into PIP and PIP2. The general topic of axon-myelin transfer of phospholipids and phospholipid precursors is reviewed.

Animals↗