Evidence that the effect of soya bean phosphatidylinositol-cholesterol-cyclosporin liposomes on the biosynthesis of acidic phospholipids in isolated subcellular membranes from rat liver and heart is attributable to the soya bean phosphatidylinositol-cholesterol liposomes

Abstract

This study examined the effect of adding soya bean phosphatidylinositol-cholesterol (2:1 molar ratio) liposomes and soya bean phosphatidylinositol-cholesterol (2:1 molar ratio)-cyclosporin liposomes on the biosynthesis of [³H]polyglycerophosphatides (phosphatidylglycerolphosphate, phosphatidylglycerol and cardiolipin) and [³H]phosphatidylinositol in mitochondria and microsomes, respectively, isolated from rat liver and heart. the results obtained with liposomes, and liposomes containing cyclosporin, established that cyclosporin did not participate in the metabolism of acidic phospholipids. In rat liver and heart mitochondria the amount of biosynthesized [³H]polyglycerophosphatides fell to one-third and a half respectively in comparison with the amounts found when liposomes were not added. the composition of [³H]polyglycerophosphatides in both mitochondria showed an increased accumulation of [³H]phosphatidylglycerolphosphate with a concomitant decrease of about 30 per cent in [³H]phosphatidylglycerol. the biosynthesis of [³H]phosphatidylinositol in both rat liver and rat heart microsomes fell to one-third of that found in the absence of liposomes. Under similar conditions the biosynthesis of [³H]cardiolipin decreased by 50 per cent in both mitochondria.

The incubation of the same liposomes and liposomes containing cyclosporin with isolated rat liver mitochondria and microsomes released about 5–7 per cent of the linoleic acid. When a corresponding amount of linoleic acid was added to the incubation mixture, the biosynthesis of [³H]polyglycerophosphatides in rat liver did not change significantly, whereas in rat heart mitochondria this biosynthesis decreased by about 33 per cent. Under these conditions, the accumulation of [³H]phosphatidylglycerolphosphate and the decrease of [³H]phosphatidylglycerol was established. the biosynthesis of [³H]phosphatidylinositol in the presence of linoleic acid in rat liver and rat heart microsomes was significantly reduced. Under similar conditions the addition of stearic acid did not significantly affect the level or composition of biosynthesized [³H]polyglycerophosphatides or biosynthesized [³H]phosphatidylinositol.