Effects of ionophore A23187 and Ba++ ions on labelling of phospholipids in rat pancreatic islets.
Ionophore A23187, either in the presence or absence of added Ca2+ or Mg2+, caused a marked accumulation of [32P]-phosphatidic acid in pancreatic islets pre-labelled with 32 Pi. A similar effect was observed following the addition of 4 mM Ba2+ ions in the absence of added Ca2+. Neither agent caused a significant modification of labelling in other lipid fractions, although there was a persistent trend towards reduced labelling of phosphatidylcholine and phosphatidylethanolamine. Ionophore A23187 also potentiated the incorporation of 3H-glycerol into phosphatidic acid and reduced the incorporation of this precursor into phosphatidylcholine. In islets pre-labelled with 3H-glycerol and subsequently exposed to A23187 or Ba2+, no significant changes were observed in label associated with either phospholipids or neutral glycerolipids. These results suggest that ionophore A23187 and Ba2+ ions can divert the synthesis of phospholipids resulting in increased formation of phosphatidic acid at the expense of non-acidic phospholipids, principally phosphatidylcholine. We tentatively suggest that this effect may be the result of inhibition by Ca2+ of the breakdown of phosphatidic acid to diglyceride, an enzymic step which may regulate the relative amounts of acidic and neutral phospholipids.
D000818:Animals; D001464:Barium / Q000494:pharmacology*; D000001:Calcimycin / Q000494:pharmacology*; D005990:Glycerol / Q000378:metabolism; D066298:In Vitro Techniques; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D010712:Phosphatidic Acids / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism*; D051381:Rats; D013997:Time Factors
D010712:Phosphatidic Acids; D010743:Phospholipids; D001464:Barium; D000001:Calcimycin; D005990:Glycerol