Mass spectrometric identification and quantitation of arachidonate-containing phospholipids in pancreatic islets: prominence of plasmenylethanolamine molecular species.
D-Glucose induces insulin secretion from beta-cells of pancreatic islets by processes involving glycolytic metabolism and generation of ATP. Glucose also induces hydrolysis of beta-cell membrane phospholipids and accumulation of nonesterified arachidonate, which facilitates Ca2+ entry and the rise in beta-cell Ca2+ concentration that is a critical signal in the induction of insulin secretion. Glucose-induced hydrolysis of arachidonate from beta-cell phospholipids is mediated in part by an ATP-stimulated, Ca(2+)-independent (ASCI)-phospholipase A2 (PLA2), which, in vitro, prefers plasmalogen over diacylphospholipid substrates, but it is not known whether islets contain plasmalogens. We have identified and quantitated the major species of arachidonate-containing phospholipids in pancreatic islets by high-performance liquid chromatographic and mass spectrometric analyses. Arachidonate has been found to constitute 30% of the total islet glycerolipid fatty acyl mass. Ethanolamine phospholipids contain 30% of total islet arachidonate, and 44% of that amount resides in three plasmenylethanolamine molecular species with residues of palmitic, oleic, or stearic aldehydes in the sn-1 position. These endogenous islet plasmenylethanolamine species are hydrolyzed more rapidly than phosphatidylethanolamine species by islet ASCI-PLA2 in vitro and are also hydrolyzed in intact islets stimulated with secretagogues. ASCI-PLA2-catalyzed hydrolysis of islet plasmenylethanolamine species in vitro is inhibited by a selective haloenol lactone suicide substrate (HELSS) which is sterically similar to plasmalogens, and HELSS also inhibits all temporal phases of both eicosanoid release and insulin secretion from secretagogue-stimulated pancreatic islets. Islet beta-cell ASCI-PLA2-catalyzed hydrolysis of arachidonate from endogenous plasmenylethanolamine substrates may be an intermediary biochemical event in the induction of insulin secretion.
Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110.
S
S
Ramanadham
A
A
Bohrer
M
M
Mueller
P
P
Jett
R W
RW
Gross
J
J
Turk
D000818:Animals; D016718:Arachidonic Acid / Q000032:analysis* / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D005947:Glucose / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D008297:Male; D013058:Mass Spectrometry; D010714:Phosphatidylethanolamines / Q000032:analysis; D010741:Phospholipases A / Q000378:metabolism; D054467:Phospholipases A2; D010743:Phospholipids / Q000032:analysis* / Q000378:metabolism; D010955:Plasmalogens / Q000032:analysis / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
D007328:Insulin; D010714:Phosphatidylethanolamines; D010743:Phospholipids; D010955:Plasmalogens; C020791:phosphatidal ethanolamines; D016718:Arachidonic Acid; D010741:Phospholipases A; D054467:Phospholipases A2; D005947:Glucose