Effect of Essential Phospholipids on the ATPases and on the Fluidity of Liver Plasma Membranes

Abstract

Essential phospholipids (EPL), rich in dilinoleoylphosphatidylcholine, were applied orally to young (40 – 80 d) and old (780 – 800 d) rats. The double ¹⁴C/³²P-labelled dilinoleoyl-phosphatidylcholine was incorporated to different degrees into the organs of the animals and particularly into plasma membranes of liver cells. Old animals incorporated a higher amount of radioactivity than young ones. The ¹⁴C/³²P ratio of the incorporated radioactivity was lower than in the administered EPL-substance. The activity of the (Na⁺−K⁺)-ATPase of rat liver plasma membranes of old animals increased after pretreatment with EPL. The thermostability of the Mg⁺⁺- and (Na⁺-K⁺)-ATPases was increased in old animals treated with EPL. EPL further caused a significant decrease of the cholesterol content and an increase of membrane fluidity parallel with the amount of incorporated EPL. This increase of fluidity was also found in spin-labeled liposomes consisting either of dipalmitoyl phosphatidylcholine or of total lipids from isolated rat liver plasma membranes and of EPL. The range of the lipid:EPL ratio tested was between 100 : 1 and 1 : 100 (w / w). The minimal concentration of EPL causing an increase in membrane fluidity detectable by the spin label technique was 2 per cent of weight of the total lipid in the liposomes.