Electrospray Ionization Mass Spectrometric Analyses of Phospholipids from Rat and Human Pancreatic Islets and Subcellular Membranes:  Comparison to Other Tissues and Implications for Membrane Fusion in Insulin Exocytosis

Ramanadham, Sasanka; Hsu, Fong‐Fu; Bohrer, Alan; Nowatzke, William; Ma, Zuchang; Turk, John

doi:10.1021/bi9722507

Cited by 77 publications

(81 citation statements)

References 58 publications

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“…Upon activation, iPLA 2 ␤ hydrolyzes the sn-2 substituent from phospholipids substrates, such as phosphatidylcholine, to yield a free fatty acid and a lysophospholipid, such as LPC (44,54,55). Because arachidonate is the most abundant sn-2 substituent in ␤-cell membrane phospholipids (23,25,26), activation of iPLA 2 ␤ upon stimulation of islets with glucose results in liberation of arachidonate as the preponderant free fatty acid (7). Stably transfected INS-1 cells that overexpress iPLA 2 ␤ (INS1-iPLA 2 ␤) exhibit amplified insulin secretory responses to glucose and other secretatogues (21,56).…”

Section: Resultsmentioning

confidence: 99%

“…The phospholipid content of esterified AA is higher in pancreatic islets than in other tissues (23,25,26,29), and arachidonate is hydrolyzed from phospholipids upon stimulation of islets with secretagogues (13,14,27,31,36,44) and accumulates to micromolar concentrations (7,27,28) that are sufficient to modulate delayed rectifier Kv channel FIGURE 5. Effects of the muscarinic agonist carbachol on INS-1 cell-delayed rectifier currents.…”

Section: Discussionmentioning

confidence: 99%

“…Arachidonate is the most abundant sn-2 substituent of islet phospholipids from rodents and humans (23,25,26) and accumulates to greater levels than do other fatty acids in secretagogue-stimulated islets (7,27). The iPLA 2 ␤ enzyme is expressed by islets from rats, mice, and humans (20, 24 -26) and by several insulinoma cell lines (31,52,53), and iPLA 2 ␤ catalyzes the hydrolysis of the sn-2 ester bond of phospholipids to yield a free fatty acid, such as arachidonic acid, and a 2-lysophospholipid, such as LPC (54,55).…”

Section: Discussionmentioning

confidence: 99%

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Modulation of the Pancreatic Islet β-Cell-delayed Rectifier Potassium Channel Kv2.1 by the Polyunsaturated Fatty Acid Arachidonate

Jacobson

Weber

Bao

et al. 2007

Journal of Biological Chemistry

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Glucose stimulates both insulin secretion and hydrolysis of arachidonic acid (AA) esterified in membrane phospholipids of pancreatic islet ␤-cells, and these processes are amplified by muscarinic agonists. Here we demonstrate that nonesterified AA regulates the biophysical activity of the pancreatic islet ␤-cell-delayed rectifier channel, Kv2.1. Recordings of Kv2.1 currents from INS-1 insulinoma cells incubated with AA (5 M) and subjected to graded degrees of depolarization exhibit a significantly shorter time-to-peak current interval than do control cells. AA causes a rapid decay and reduced peak conductance of delayed rectifier currents from INS-1 cells and from primary ␤-cells isolated from mouse, rat, and human pancreatic islets. Stimulating mouse islets with AA results in a significant increase in the frequency of glucoseinduced [Ca 2؉ ] oscillations, which is an expected effect of Kv2.1 channel blockade. Stimulation with concentrations of glucose and carbachol that accelerate hydrolysis of endogenous AA from islet phosphoplipids also results in accelerated Kv2.1 inactivation and a shorter time-to-peak current interval. Group VIA phospholipase A 2 (iPLA 2 ␤) hydrolyzes ␤-cell membrane phospholipids to release nonesterified fatty acids, including AA, and inhibiting iPLA 2 ␤ prevents the muscarinic agonist-induced accelerated Kv2.1 inactivation. Furthermore, glucose and carbachol do not significantly affect Kv2.1 inactivation in ␤-cells from iPLA 2 ␤ ؊/؊ mice. Stably transfected INS-1 cells that overexpress iPLA 2 ␤ hydrolyze phospholipids more rapidly than control INS-1 cells and also exhibit an increase in the inactivation rate of the delayed rectifier currents. These results suggest that Kv2.1 currents could be dynamically modulated in the pancreatic islet ␤-cell by phospholipase-catalyzed hydrolysis of membrane phospholipids to yield non-esterified fatty acids, such as AA, that facilitate Ca 2؉ entry and insulin secretion.Glucose metabolism within the pancreatic islet ␤-cell generates a multitude of signals that regulate insulin secretion. Changes in the relative concentrations of the metabolites ATP and ADP cause ␤-cell depolarization via closure of ATP-sensitive potassium channels (K ATP ), 3 which results in activation of voltage-operated Ca 2ϩ channels, Ca 2ϩ influx, and insulin secretion (1). The extent of ␤-cell depolarization and insulin release are regulated in part by the activation of repolarizing ion channels, including the voltage-gated potassium channel, Kv2.1 (2-4). One mechanism employed by pancreatic ␤-cells to regulate the biophysical activity of the ion channels involved in insulin release involves hydrolysis of membrane phospholipids to yield mediators that include inositol triphosphates and free fatty acids (5-8).Pharmacologic, biochemical, and genetic evidence suggests that glucose-stimulated hydrolysis of esterified arachidonic acid from ␤-cell membrane phospholipids is required for physiological insulin secretion (7-25). Pancreatic islet ␤-cells contain high levels of arachidonic ac...

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Modulation of the Pancreatic Islet β-Cell-delayed Rectifier Potassium Channel Kv2.1 by the Polyunsaturated Fatty Acid Arachidonate

Jacobson

Weber

Bao

et al. 2007

Journal of Biological Chemistry

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“…Ca 2ϩ -independent Phospholipase A 2 Activity Assay-Tissue Ca 2ϩ -independent PLA 2 specific activity was determined as described (8) (17)(18)(19). Glycerophosphocholine (GPC) lipids and triacylglycerols (TAGs) were analyzed as [MϩLi] ϩ ions.…”

Section: Methodsmentioning

confidence: 99%

Male Mice That Do Not Express Group VIA Phospholipase A2 Produce Spermatozoa with Impaired Motility and Have Greatly Reduced Fertility

Bao¹,

Miller

et al. 2004

Journal of Biological Chemistry

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157

178

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The Group VIA Phospholipase A 2 (iPLA 2 ␤) is the first recognized cytosolic Ca 2؉ -independent PLA 2 and has been proposed to participate in arachidonic acid (20:4) incorporation into glycerophosphocholine lipids, cell proliferation, exocytosis, apoptosis, and other processes. To study iPLA 2 ␤ functions, we disrupted its gene by homologous recombination to generate mice that do not express iPLA 2 ␤. Heterozygous iPLA 2 ␤ ؉/؊ breeding pairs yield a Mendelian 1:2:1 ratio of iPLA 2 ␤ ؉/؉ , iPLA 2 ␤ ؉/؊ , and iPLA 2 ␤ ؊/؊ pups and a 1:1 male:female gender distribution of iPLA 2 ␤ ؊/؊ pups. Several tissues of wild-type mice express iPLA 2 ␤ mRNA, immunoreactive protein, and activity, and testes express the highest levels. Testes or other tissues of iPLA 2 ␤ ؊/؊ mice express no iPLA 2 ␤ mRNA or protein, but iPLA 2 ␤ ؊/؊ testes are not deficient in 20:4-containing glycerophosphocholine lipids, indicating that iPLA 2 ␤ does not play an obligatory role in formation of such lipids in that tissue. Spermatozoa from iPLA 2 ␤ ؊/؊ mice have reduced motility and impaired ability to fertilize mouse oocytes in vitro and in vivo, and inhibiting iPLA 2 ␤ with a bromoenol lactone suicide substrate reduces motility of wild-type spermatozoa in a time-and concentration-dependent manner. Mating iPLA 2 ␤ ؊/؊ male mice with iPLA 2 ␤ ؉/؉ , iPLA 2 ␤ ؉/؊ , or iPLA 2 ␤ ؊/؊ female mice yields only about 7% of the number of pups produced by mating pairs with an iPLA 2 ␤ ؉/؉ or iPLA 2 ␤ ؉/؊ male, but iPLA 2 ␤ ؊/؊ female mice have nearly normal fertility. These findings indicate that iPLA 2 ␤ plays an important functional role in spermatozoa, suggest a target for developing male contraceptive drugs, and complement reports that disruption of the Group IVA PLA 2 (cPLA 2 ␣) gene impairs female reproductive ability.

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“…Many studies have demonstrated that PtdEtn molecular species can readily be analyzed by negative-ion ESI/MS [23,[32][33][34][35] since these species become negatively charged after the facile loss of a proton from the head group of PtdEtn under alkaline conditions (i.e., conjugate acid). Thus, there are some similarities in electrical properties between ethanolamine glycerophospholipids and anionic phospholipids when alkali media conditions are employed.…”

Section: The Effects Of Alkalization Of the Infusion Solution On Intrmentioning

confidence: 99%

Factors influencing the electrospray intrasource separation and selective ionization of glycerophospholipids

Han

Yang

et al. 2006

J. Am. Soc. Mass Spectrom.

119

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The external electric field induces a separation of cations from negative electrolyte ions in the infusate while differential ionization of molecular species that possess differential electrical propensities can be induced in either the positive-or negative-ion mode during the electrospray ionization process. These physical and electrical processes that occur in the electrospray ion source have been used to selectively ionize lipid classes possessing different electrical propensities that are now known as "intrasource separation and selective ionization". However, the chemical principles underlying charge-dependent alterations in ionization efficiencies responsible for the selective ionization of lipid classes are not known with certainty. Herein, we examined the multiple factors that contribute to intrasource separation and selective ionization of lipid classes under optimal instrumental conditions. We demonstrated that many different lipid classes could be selectively ionized in the ion source and that intrasource resolution of distinct molecular constituents was independent of lipid concentration, flow rate, and residual ions under most experimental conditions. Moreover, the presence of alkaline conditions facilitates the selective ionization of many lipid classes through a mechanism independent of the design of the ESI ion source. Collectively, this study provides an empirical foundation for understanding the chemical mechanisms underlying intrasource separation and selective ionization of lipid classes that can potentially be used for global analysis of cellular lipidomes without the need for chromatographic separation. (J Am Soc Mass Spectrom 2006, 17, 264 -274)

show abstract

Electrospray Ionization Mass Spectrometric Analyses of Phospholipids from Rat and Human Pancreatic Islets and Subcellular Membranes: Comparison to Other Tissues and Implications for Membrane Fusion in Insulin Exocytosis

Cited by 77 publications

References 58 publications

Modulation of the Pancreatic Islet β-Cell-delayed Rectifier Potassium Channel Kv2.1 by the Polyunsaturated Fatty Acid Arachidonate

Modulation of the Pancreatic Islet β-Cell-delayed Rectifier Potassium Channel Kv2.1 by the Polyunsaturated Fatty Acid Arachidonate

Male Mice That Do Not Express Group VIA Phospholipase A2 Produce Spermatozoa with Impaired Motility and Have Greatly Reduced Fertility

Factors influencing the electrospray intrasource separation and selective ionization of glycerophospholipids

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