Protein–Lipid Composition of Plasma Membranes and Structural Organization of the Cytoskeleton in Nucleated Erythrocytes of Cartilaginous and Teleost Fish

<p>This study compares erythrocyte membrane composition in two cartilaginous Black Sea fish (<em>Raja clavata, Dasyatis</em> <em>pastinaca</em>) and three teleosts (<em>Scorpaena porcus, Spicara flexuosa, Trachurus mediterraneus ponticus</em>). Cartilaginous fish displayed a higher protein-to-lipid ratio, whereas teleosts showed relatively more membrane lipids. The main phospholipids were phosphatidylcholine (PC) and phosphatidylethanolamine (PEA), with phosphatidylserine (PS), monophosphoinositides (MPI), and sphingomyelin (SM) also present. Fatty acid profiles were similar between the two cartilaginous species, with docosahexaenoic acid (DHA) dominant and three times more abundant in <em>D. pastinaca</em> than in <em>R. clavata.</em> In teleosts, DHA levels were comparable, but total unsaturated fatty acids varied (<em>S. porcus</em> < <em>T. mediterraneus ponticus</em> < <em>S. flexuosa</em>). The unsaturation coefficient showed the same trend and was lowest in cartilaginous fish. Published data indicate that nucleated fish erythrocytes possess a more complex cytoskeleton than mammalian anucleate erythrocytes, reflecting different evolutionary adaptations in membrane mechanics.</p>