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G Y Sun

Publications and source records attributed to G Y Sun.

At least 55 records · Page 3Linked to original sources
PubMed1995

In utero hypoxic ischemia decreases the cholinergic agonist-stimulated poly-phosphoinositide turnover in the developing rat brain.

Perinatal hypoxic-ischemic (HI) insult is known to cause cellular and molecular disturbances leading to functional and behavioral abnormalities during brain development. In this study, we examined the effects of an in utero HI insult on poly-phosphoinositide turnover in vivo in the cerebrum and cerebellum as well as cholinergic-stimulated turnover in cortical slices from developing rat brain. In utero HI treatment was carried out by clamping the uterine blood vessels of near-term fetuses for 5, 10 and 15 min followed by resuscitation of the newborn pups. The in vivo protocol for examining poly-PI signaling activity in 2 week-old pup brain involved intracerebral injection of [3H]inositol for 16 hr and subsequent intraperitoneal injection with lithium (8 meq/kg) for 4 hr prior to decapitation. In the control pups, lithium elicited a 2.6 fold increase in labeled inositol phosphate (IP) in the cerebrum as compared to a 1.3 fold increase in the cerebellum. In utero HI insult (5 to 15 min) resulted in a small increase in labeled IP in the cerebrum but not in the cerebellum. Carbachol stimulation of poly-PI turnover was examined in brain slices prelabeled with [3H]inositol in vivo. Incubation of the prelabeled slices with carbachol in the presence of LiCl (10 mM) resulted in a time-, dose- and age-dependent increase in labeled IP. Brain slices from 2 week-old pups that experienced in utero HI-treatment for 10 and 15 min (but not 5 min) showed a significant decrease in carbachol-stimulation of labeled IP as compared with control pups. These results indicate the effects of in utero HI on the choninergic-stimulated poly-PI signaling pathway and its implication on related functional deficits in the developing brain.

Animals↗
PubMed1995

Regulation of FFA by the acyltransferase pathway in focal cerebral ischemia-reperfusion.

Cerebral insult is associated with a rapid increase in free fatty acids (FFA) and arachidonic acid release has been linked to the increase in eicosanoid biosynthesis. In transient focal cerebral ischemia induced by middle cerebral artery (MCA) occlusion, there is an inverse relationship between the increase in FFA and the decrease in ATP, both during the ischemia period and at later time periods after reperfusion. In this study, the focal cerebral ischemia model was used to examine incorporation of [14C]arachidonic acid into the glycerolipids in rat MCA cortex at different reperfusion times after a 60 min ischemia. The label was injected intracerebrally into left and right MCA cortex 1 hr prior to decapitation. Labeled arachidonic acid was incorporated into phosphatidylcholine, phosphatidylethanolamine and neutral glycerides. With increasing time (4-16 hr) after a 60 min ischemia, an inhibition of labeled arachidonate uptake could be found in the right ischemic MCA cortex, whereas the distribution of radioactivity among the major phospholipids was not altered. When compared to labeled PC, there was a 3-4 fold increase in incorporation of label into phosphatidic acid and triacylglycerols (TG) in the right MCA cortex, suggesting of an increase in de novo biosynthesis of TG. In an in vitro assay system, synaptosomal membranes isolated from MCA cortex 8 and 16 hr after a 60 min ischemia showed a significant decrease in arachidonoyl transfer to lysophospholipids, due mainly to a decrease in lysophospholipid:acylCoA acyltransferase activity. Assay of phospholipase A2 activity with both syaptosomes and cytosol, however, did not show differences between left and right MCA cortex or with time after reperfusion. These results suggest that besides ATP availability, the decrease in acyltransferase activity may also contribute to the increase in FFA in cerebral ischemia-reperfusion.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1995

Stimulation of group II phospholipase A2 mRNA expression and release in an immortalized astrocyte cell line (DITNC) by LPS, TNF alpha, and IL-1 beta. Interactive effects.

Astrocytes are immunoactive cells in brain and have been implicated in the defense mechanism in response to external injury. Previous studies using cultured glial cells indicated the ability of astrocytes to respond to bacteria endotoxin and cytokines, resulting in the release of phospholipase A2. In this study, we examined the interactive effects of lipopolysaccharides (LPS), interleukin 1 beta (IL-1 beta) and tumor necrosis factor (TNF alpha) to stimulate phospholipase A2 (PLA2) in an immortalized astrocyte cell line (DITNC) with many properties of type I astrocytes. Northern blot analysis using oligonucleotide probes derived from the cDNA encoding the rat spleen group II PLA2 indicated the ability of DITNC cells to respond to all three factors in the induction of gene expression and the release of PLA2. After an initial lag time of 2 h, PLA2 release was proportional to time, reaching a plateau by 12 h. This event occurred at a time period preceding any signs of cell death. Cycloheximide at 1.25 microM completely inhibited cytokine-induced PLA2 release. When suboptimal amounts of TNF alpha were added to the DITNC culture together with IL-1 beta or LPS, a synergistic increase in the induction of PLA2 release could be observed. On the other hand, combination of IL-1 beta and LPS resulted only in an additive increase in PLA2 release. Antibodies to IL-1 beta and TNF alpha completely neutralized the effects of these two agents on PLA2 release. However, neither antibody was able to inhibit the PLA2 release induced by LPS, suggesting that the effect of LPS was not complicated by the release of IL-1 beta or TNF alpha. Taken together, results show that the immortalized astrocyte cell line (DITNC) can be used for studies to elucidate the molecular mechanism underlying the cytokine signaling cascade and subsequent induction of PLA2 synthesis.

Animals↗
PubMed1995

In situ hybridization of mRNA expression for IP3 receptor and IP3-3-kinase in rat brain after transient focal cerebral ischemia.

Loss of intracellular calcium homeostasis has been regarded an important factor underlying neuron cell death after cerebral ischemic insult. In the brain, a major mechanism for regulation of intracellular calcium is through the signal transduction pathway involving hydrolysis of poly-phosphoinositides and release of the second messenger, inositol 1,4,5-trisphosphate (IP3). IP3 mobilizes calcium by interacting with an intracellular receptor. Upon its release after agonist stimulation, this second messenger is catabolized by a 3-kinase and a 5-phosphatase. In this study, in situ hybridization was carried out to examine the mRNA expression of IP3, receptor (IP3R) and IP3 3-kinase (IP3K) in rat brain cortex after transient focal cerebral ischemia induced by temporary occlusion of the middle cerebral artery (MCA) and the common carotid arteries (CCAs). Results indicate a large decrease (52%) in IP3R mRNA levels in the ischemic cortex as compared to that in the contralateral side at 4 h after a 45 min ischemic insult. By 16 h, practically no IP3R mRNA could be detected in the ischemic cortex. On the other hand, IP3K mRNA levels remained unaltered until 16 h after reperfusion, during which time, expression in the infarct core decreased but that surrounding the core area increased instead. Hybridization of adjacent brain sections with probes for neuron specific enolase (NSE) and beta-actin indicated also a time-dependent decrease in mRNA levels after ischemia, but these changes were less dramatic as compared to IP3R. At 16 and 24 h after reperfusion, there was an increase in beta-actin mRNA in cortical areas outside the MCA cortex, suggesting of reactive gliosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Increased inositol 1,4,5-trisphosphate accumulation correlates with an up-regulation of bradykinin receptors in Alzheimer's disease.

An alteration in signal transduction systems in Alzheimer's disease (AD) would likely be of pathophysiological significance, because these processes control normal brain functions. Previously, a diminished beta-adrenergic-mediated cyclic AMP response was found in cultured fibroblasts from AD patients. Because cross-talk between the phosphoinositide and cyclic AMP pathways exists, the phosphoinositide cascade was studied under conditions that were similar to those for studying the cyclic AMP response. Cells from AD patients and age-matched controls responded to bradykinin (BK) and released inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] in a time- and dose-dependent manner. The level of Ins(1,4,5)P3 increased rapidly and transiently in response to BK, peaked at 5 s, but still remained 116-132% above the basal level by 30 s. Although the temporal patterns were similar in both groups, the Ins(1,4,5)P3 concentrations in AD fibroblasts were 73 and 89% above levels in the age-matched controls at 5 and 10 s, respectively. Prostaglandin E1 also increased Ins(1,4,5)P3 formation, but this response was not different between the two groups. Although KD (affinity) values for the BK receptor were similar in both control and AD cells, the number of BK receptors (Bmax) was significantly elevated in AD fibroblasts (186.8 +/- 0.8 fmol/mg of protein) as compared with control fibroblasts (57.2 +/- 15.3 fmol/mg of protein). These results indicate that the elevated Ins(1,4,5)P3 production in response to BK in AD fibroblasts is positively correlated with an increase in the receptor numbers.

Aged↗
PubMed1995

Free fatty acids, neutral glycerides, and phosphoglycerides in transient focal cerebral ischemia.

Cerebral ischemia is known to cause an increase in levels of free fatty acids (FFAs) and diacylglycerols (DGs), although the mechanism(s) leading to these changes is not well understood. In this study, we examined FFA and DG levels along with those of other lipids in rats during and after transient focal cerebral ischemia induced by temporary occlusion of the right middle cerebral artery (MCA) and both common carotid arteries. During the duration of ischemia (15-60 min), there was a time-dependent increase (two- to 10-fold) in FFA levels in the right MCA cortex, whereas levels of DG and other lipids were not altered appreciably. FFA levels in right MCA cortex returned to near control values after reperfusion. However, following a 60-min ischemic insult, there was a second phase of FFA level increase that was evident after 16 h. The FFAs accumulated during the ischemia period were different from those after reperfusion, suggesting differences in mechanisms for their release. During the second phase of FFA release, there were increases in levels of DGs and triacylglycerols (TGs) with unusually high proportions of 20:4(n-6) and 22:6(n-3). The increases in FFA, DG, and TG levels were marked by a decrease in content of phosphoglycerides (PGs). It is interesting that the increases in levels of FFAs and neutral glycerides accounted only for 10% of the total PGs depleted. The lipid changes during this reperfusion period correlated well with the development of cortical infarct.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Inositol trisphosphate, polyphosphoinositide turnover, and high-energy metabolites in focal cerebral ischemia and reperfusion.

BACKGROUND AND PURPOSE: Although the signaling pathway involving polyphosphoinositide (poly-PI) hydrolysis and release of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] is an important mechanism for regulation of neuronal calcium homeostasis, the effect of cerebral ischemia-reperfusion on this calcium signaling pathway is not well understood. Because activity of this pathway is dependent on availability of ATP, this study is aimed at examining the poly-PI signaling pathway and high-energy metabolites in a rat stroke model. METHODS: Focal cerebral ischemia in rats was induced by temporary occlusion of the right middle cerebral artery and both common carotid arteries. Levels of Ins(1,4,5)P3 were determined by use of the radioreceptor binding assay. Poly-PI turnover in rat cortex was assessed with an in vivo protocol involving intracerebral injection of [3H] inositol and systemic administration of lithium. High-energy metabolites (ATP, ADP, and AMP) were analyzed by high-performance liquid chromatography. RESULTS: Ischemia induced an increase in poly-PI turnover in the right middle cerebral artery cortex, but reperfusion led to a decline in this signaling activity. However, Ins(1,4,5)P3 levels decreased during ischemia, and these levels were not restored if ischemic insults were longer than 30 minutes. ATP levels decreased to 26% of control during ischemia and recovered to 80% of control during the initial 4 hours of reperfusion; these changes were followed by a second phase of decline. CONCLUSIONS: Results show an important relationship between ischemia-induced depletion of high-energy metabolites and poly-PI signaling activity. However, the uncoupling between Ins(1,4,5)P3 and ATP during reperfusion after severe ischemia suggests that metabolism of Ins(1,4,5)P3 is more stringently regulated than ATP.

Adenosine Diphosphate↗
PubMed1995

Stimulation of phospholipase A2 expression in rat cultured astrocytes by LPS, TNF alpha and IL-1 beta.

Results from this study are in good agreement with those reported by Oka and Arita (1991) who demonstrated induction of PLA2 mRNA expression in primary astrocytes in response to LPS, TNF alpha and IL-1 beta. In general, the increase in PLA2 mRNA correlated well with the extent of PLA2 secretion into the culture medium. Using the immortalized astrocyte cell line (DITNC), similar induction of PLA2 mRNA expression and secretion of the enzyme into the culture medium could be observed. The lack of hydrolysis of labeled PI to DG further confirmed the specificity of cytokine induction of PLA2 release into the culture medium. By comparing the time course for PLA2 release with that for LDH release, it can be concluded that cytokine induction of PLA2 release is not related to events accompanying cell death due to serum deprivation. Although it has been well demonstrated that exposure of astrocytes to LPS can induce the synthesis and release of TNF alpha and IL-1 beta, the mechanism underlying this event has not been elucidated (Lieberman et al., 1989). Furthermore, how LPS as well as other cytokines induce the mRNA expression and secretion of PLA2 remains to be investigated. The availability of the immortalized astrocyte cell line (DITNC) will be a useful tool for this type of study. These cells are easy to culture and large preparations can be obtained. In addition, these cells will be useful as a model to relate the effects of cytokines on other cellular and metabolic events that may be directly or indirectly linked to the PLA2 cascade.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Phosphorylation of lipids in rat primary glial cells and immortalized astrocytes (DITNC).

Phosphatidylinositol 4,5-bisphosphate, a substrate in the signal transduction pathway involving phospholipase C, is synthesized in cell membranes by phosphorylation of phosphatidylinositol (PI) and phosphatidylinositol 4-phosphate (PI-4-P). Incubation with [gamma-32P]adenosine triphosphate of membranes isolated from primary glial cells in culture and from an immortalized astrocyte cell line (DITNC) and subsequent separation of the lipids by high-performance thin-layer chromatography revealed a number of labeled lipid bands. Further analysis of the deacylated products by high-performance liquid chromatography indicated the presence of two PI-4-P bands and a band corresponding to lysoPIP (PIP, PI phosphate). The two PI-4-P bands were more prominent in the samples from astrocyte cell membranes than from synaptic plasma membranes and plasma membranes. Analysis of the fatty acid composition of PI by gas-liquid chromatography revealed that both 20:3n-9 and 20:4n-6 were present in PI of cultured cell membranes, whereas the brain membranes contained exclusively 20:4n-6. The two PI-4-P bands in these membranes can be attributed to the presence of different molecular species of PI. Assignment of the fraction corresponding to lysoPIP was consistent with the observation that an increase in label in this lipid band occurred upon incubation of DITNC cell supernatant with lysoPI (1-stearoyl PI). This suggests that endogenous lysoPI present in the cell membranes can be phosphorylated to form lysoPIP.

Adenosine Triphosphate↗
PubMed1993

The cholinergic receptor-linked phosphoinositide metabolism in mouse cerebrum and cerebellum in vivo.

The cholinergic receptor-linked poly-phosphoinositide hydrolysis was studied in mouse cerebrum and cerebellum after prelabeling the brain with [3H]inositol. I.p. injection of Li (8 meq/kg) to C57Bl/6J mice for 4 h resulted in 14- and five-fold increases in [3H]inositol-labeled inositol monophosphate (IP1) in cerebrum and cerebellum, respectively. The labeled inositol bisphosphate (IP2) was also increased 83 and 19% in cerebrum and cerebellum, respectively. Prior injection of atropine (100 mg/kg) resulted in inhibition of Li-induced increases in labeled IP1 by 74 and 56% in cerebrum and cerebellum, respectively. Administration of pilocarpine (20 mg/kg) to the Li-treated mice for 30 min resulted in further increases in labeled IP1 and IP2 and a concomitant decrease in labeled inositol in cerebrum but not in cerebellum. Mass measurements of IP1 and IP2 isomers by HPLC revealed that inositol 1-monophosphate (Ins(1)P), inositol 4-monophosphate (Ins(4)P) and inositol 1,4-bisphosphate (Ins(1,4)P2) were all increased by pilocarpine administration in the Li-treated mouse cerebrum. The effects of pilocarpine administration in mouse cerebrum (increases in IP1 and IP2) could be completely inhibited by preinjection of atropine. Atropine injection also decreased the levels of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3]. Surprisingly, a decrease in Ins(1,4,5)P3 level was also found in non-Li-treated mice after pilocarpine administration (30 mg/kg, 10-40 min). Except for the increase (20%) in [32P]-labeled PIP in the cerebrum, Li or Li together with pilocarpine administration did not alter the levels of [3H]inositol or [32P]phosphate-labeled phosphoinositides.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Acylation of lysophosphatidylcholine by brain membranes.

Brain microsomes catalyze the acylation of lysophosphatidylcholine (lysoPtdCho) in the presence and absence of added CoA derivatives. The catalytic activity is distributed widely in various subcellular fractions from rat or bovine cerebral cortex as measured by the conversion of 1-[14C]palmitoyl-sn-glycero-3-phosphocholine to [14C]PtdCho. Analysis of this latter compound revealed that the dipalmitoyl derivative is the predominant molecular species, which is formed in this reaction by transacylation between two [14C]lysoPtdCho molecules. This lysoPtdCho: lysoPtdCho transacylation reaction was enhanced several-fold by the addition of oleoyl-CoA, which also is an effective donor of acyl groups in the acyl-CoA: lysoPtdCho acyltransferase-catalyzed reaction. Measurements of the initial velocity of the transacylation reaction were used to determine kinetic constants. Apparent Km values for lysoPtdCho in the presence and absence of oleoyl-CoA were 29 microM and 104 microM, respectively, and the corresponding maximal velocities were 0.11 and 1.06 nmol.min-1.mg-1, respectively. Oleoyl-CoA at 4 microM produced half-maximal stimulation of the transacylation reaction. CoA also stimulated the rate of conversion of [14C]lysoPtdCho to [14C]PtdCho, either in the presence or absence of oleoyl-CoA, with a half-maximal effect of CoA at 80 microM. These results may be important in understanding the regulation of PtdCho synthesis and the mechanism by which acyl group composition of this compound is controlled.

Acylation↗
PubMed1993

Effects of focal cerebral ischemia on expression and activity of inositol 1,4,5-trisphosphate 3-kinase in rat cortex.

Results from this study clearly indicate that Ins(1,4,5)P3 3-kinase is a target enzyme of cerebral ischemia insult. This enzyme is responsible for removal of Ins(1,4,5)P3 which, in turn, plays an important role in the maintenance of intracellular Ca2+ homeostasis. Not only did a time-dependent decrease in enzyme activity occur due to the focal cerebral ischemic insult, but there was also a second phase for the decline in enzyme activity around 6 h after the insult. Examination of the mRNA for the 3-kinase in frozen brain sections suggested an increase in message at a time (around 8 h) prior to development of tissue infarct. Since the initial decline in enzyme activity during ligation correlated well with the time for development of an infarct, assay of this enzyme could be used as a biochemical marker of cerebral ischemic insult.

Animals↗
PubMed1993

Metabolism of inositol 1,4,5-trisphosphate in mouse brain due to decapitation ischemic insult: effects of acute lithium administration and temporal relationship to diacylglycerols, free fatty acids and energy metabolites.

Previous studies have shown that global cerebral ischemia induced by decapitation leads to the stimulated hydrolysis of poly-phosphoinositides. In this study, the decapitation model was used to further examine the temporal events related to metabolism of Ins(1,4,5)P3 and the release of diacylglycerols (DGs) and free fatty acids (FFAs) in the mouse brain. Since lithium administration is known to inhibit inositol monophosphatase activity in brain, the effects of acute lithium injection on Ins(1,4,5)P3 metabolism were also examined. Cerebral ischemia induced by decapitation of C57 Bl/6J mice resulted in transient increases of Ins(1,4,5)P3, Ins(1,4)P2 and Ins(4)P which peaked at 35, 65 and 125 s, respectively. The level of Ins(1)P, however, was not altered. Mice administered lithium by intraperitoneal injection (8 meq/kg for 4 h) gave rise to a 40- and 4-fold increase in levels of Ins(1)P, Ins(4)P, respectively, a 20% increase in levels of Ins(1,4)P2 but no apparent changes in the levels of Ins(1,4,5)P3. Decapitation also induced an increase in the levels of DGs and FFAs. Unlike the transient appearance of Ins(1,4,5)P3, however, DG levels increased steadily for 2 min and then reached a plateau whereas the FFAs showed a lag time of 35 s prior to a biphasic increase. During the initial 2 min after decapitation, there was a preferential increase in the DG species containing 18:0 and 20:4. Lithium administration did not alter the decapitation-induced release of DG and FFA. As expected, decapitation gave rise to a rapid decrease in the levels of phosphocreatine and ATP and the decline in ATP was marked by a transient appearance of ADP and a concomitant increase in AMP.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Fatty acids in the lipids of Drosophila heads: effects of visual mutants, carotenoid deprivation and dietary fatty acids.

Lipids of Drosophila heads were extracted and separated by high-performance thin-layer chromatography. Fatty acid compositions of major phospholipids as well as of triglycerides were analyzed by gas-liquid chromatography. Proportions of the major fatty acids (14:0, 16:0, 16:1, 18:0, 18:1, 18:2, 18:3) varied depending on the lipid analyzed. Docosahexaenoic acid (22:6), common in vertebrate photoreceptors and brain, and arachidonic acid (20:4), a precursor of eicosanoids, were lacking. A comparison of the fatty acid composition of the diet vs. the head suggested that Drosophila can desaturate but may not be able to elongate fatty acid carbon chains. Fatty acid analyses were carried out after the following visual system alterations: i) the transduction mutant where no receptor potential results from a deficit in phospholipase C; ii) an allele of eyes absent; iii) the mutant outer rhabdomeres absent which lacks visual pigment and rhabdomeres in the predominant type of compound eye receptor, rhabdomeres 1 through 6; and iv) carotenoid deprivation which reduces opsin and rhabdomere size. We also evaluated aging by comparing newly-emerged vs. aged wild-type flies. Alterations in fatty acid composition based on some of these manipulations were found. Based on comparisons between flies reared on media differing in C16 and C18, there is an indication that diet readily affects tissue fatty acid composition.

Age Factors↗
PubMed1993

Phospholipids in Drosophila heads: effects of visual mutants and phototransduction manipulations.

A procedure was developed to label phospholipids in Drosophila heads by feeding radioactive phosphate (32Pi). High-performance thin-layer chromatography showed label incorporation into various phospholipids. After 24 h of feeding, major phospholipids labeled were phosphatidylethanolamine (PE), 47%; phosphatidylcholine (PC), 24%; and phosphatidylinositol (PI), 12%. Drosophila heads have virtually no sphingomyelin as compared with mammalian tissues. Notable label was in ethanolamine plasmalogen, lysophosphatidylethanolamine, lysophosphatidylcholine and lysophosphatidylinositol. Less than 1% of the total label was in phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate. Other lipids labeled included phosphatidylserine, phosphatidic acid and some unidentified lipids. A time course (3-36 h) study revealed a gradual decrease in proportion of labeled PI, an increase in proportion of labeled PC and no obvious change in labeled PE. There were no significant differences in phospholipid labeling comparing the no receptor potential (norpA) visual mutant and wild type under light vs. dark conditions. However, overall 32P labeling was higher in the wild type fed in the light as compared to the dark and to norpA either in light or dark. This suggests that functional vision facilitates incorporation of label. Differences in phospholipid labeling were observed between young and aged flies, particularly in lysophospholipids and poly-PI, implicating phospholipase A2 function in recycling. v Manipulations such as the outer rhabdomeres absent and eyes absent mutants and carotenoid deprivation failed to yield notable differences in phospholipid labeling pattern, suggesting that phospholipids important to vision may constitute only a minor portion of the total labeled pool in the head.

Animals↗
PubMed1993

Manganese exposure to PC-12 cells alters triacylglycerol metabolism and promotes neurite outgrowth.

Exposure of PC-12 cells to MnCl2 (10-100 microM for 1 to 3 days) resulted in both morphological and metabolic changes as indicated by promotion of neurite outgrowth and an increased incorporation of labeled fatty acids (14:0, 18:1 and 20:4) into triacylglycerols (TG). Cells prelabeled with [14C]arachidonic acid (AA) showed a time-dependent decrease in labeled TG, and the rate of decline was inhibited by Mn (100 microM). In the pulse-chase type of study, the decrease in the proportion of labeled TG as well as labeled phosphatidylcholine (PC) was marked by an increase in labeled phosphatidylinositol and phosphatidylethanolamine. These results support previous notion that TG plays an important role in channeling the fatty acid nutrients for biosynthesis of membrane phospholipids. Thus, the Mn-induced inhibition of the ability to transfer TG fatty acids to other lipids in PC-12 cells may be an underlying cause for the observed morphological changes.

Animals↗
PubMed1993

Effects of lysophospholipids and diacylglycerols on the transfer of arachidonic acid to phospholipids and triacylglycerols in rat brain membranes.

Brain membranes catalyze the acylation of lysophospholipids and diacylglycerols (DAG) to form the respective phospholipids and triacylglycerols (TAG). These acylation reactions were examined using brain plasma membrane-enriched fractions by measuring the incorporation of [14C]arachidonic acid into TAG and individual phospholipids under a variety of conditions. In the absence of added lipid substrates, the amount of [14C]arachidonic acid incorporated into TAG in the presence of ATP, Mg2+, and CoA was approx twice the amount incorporated into phosphatidylositol (PtdIns), and more than 10 times the amount incorporated into phosphatidylcholine (PtdCho), phosphatidylethanolamine (PtdEtn) and phosphatidylserine (PtdSer). These results suggest the presence of endogenous DAG, lysoPtdIns, and the required enzymes in the membrane preparations for acylation reactions. The addition of DAG, lysoPtdCho or lysoPtdIns to the incubation system resulted in a 2-20-fold increase in the rate of incorporation of labeled arachidonic acid into TAG, PtdCho or PtdIns, respectively. LysoPtdEtn and lysoPtdSer were poor substrates for the synthesis of PtdEtn and PtdSer. On the other hand, the addition of lysoPtdSer stimulated the incorporation of [14C]arachidonic acid into TAG and into most phospholipids, especially phosphatidic acid, the synthesis of which was enhanced more than 10-fold. Exogenous lysoPtdCho and lysoPtdIns inhibited the incorporation of [14C]arachidonate into TAG in the presence of DAG, and DAG inhibited the incorporation of [14C]arachidonic acid into phospholipids in the presence of lysophospholipids. In general, [14C]palmitic acid was less effectively incorporated into lipids than arachidonic acid. These results suggest reciprocal regulatory effects of DAG and lysophospholipids on acyltransfer to phospholipids and triacylglycerol in brain membranes.

Adenosine Triphosphate↗