Phospholipid Fatty Acid Composition and Distribution Patterns of Prostaglandins in Malpighian Tubules of the Yellow Mealworm (Coleoptera: Tenebrionidae)

Abstract

Fatty acid compositions were determined for four phospholipid fractions (phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine-phosphatidylinositol and cardiolipin extracted from Malpighian tubules of laboratory and feral populations of the yellow mealworm, Tenebrio molitor . These compositions were compared with each other and to the fatty acid composition of standard diet used for the laboratory population. The insect lipids, but not the dietary ones, showed multiple positional isomers for the monoenoic acids, and the presence of polyunsaturated fatty acids. Among the four phospholipid classes there were distinct relative abundance differences, and for all classes except phosphatidylserine-phosphatidylinositol and cardiolipin, the feral population contained greater proportions of unsaturated fatty acids (especially polyunsaturated fatty acids) than did the laboratory population. These results indicate selective fatty acid incorporation into individual Malpighian tubule phospholipid classes. Studies with radioactive arachidonic acid using the laboratory population similarly indicate selective absorption of arachidonic acid into Malpighian tubule phospholipid classes. Under our conditions, 1.2% of total radioactivity was incorporated into the Malpighian tubule phospholipids. Within phospholipids, most of the radioactivity was associated with phosphatidylcholine (76.9%), and less with phosphatidylethanolamine (9.5%) and phosphatidyserine-phosphatidylinositol (11.9%). Very little radioactivity was recovered in cardiolipin (1.8%). Finally, immunohistochemical studies with intact Malpighian tubules of T. molitor larvae demonstrated distinctive distribution patterns for the prostaglandins PGE2 and PGF2α, which are two major cyclooxygenase products from phospholipid polyunsaturated fatty acids suspected to be involved in T. molitor renal functions.