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.
Ramanadham
S
S
Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110.
Bohrer
A
A
Mueller
M
M
Jett
P
P
Gross
R W
RW
Turk
J
J
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