Spectrin and other membrane-skeletal components in human red blood cells of different age

Background: Old human red blood cells (RBCs) have a reduced surface area with respect to young RBCs. If this decrease occurred through the release of vesicles similar to the spectrin-free vesicles that are shed in vitro under different experimental conditions or during storage, there would be no decrease of membrane-skeleton, but only of lipid bilayer surface area, during RBC ageing in vivo. However, we observed a decrease in spectrin and other membrane-skeletal proteins in old RBCs. Because RBCs contain components of the ubiquitin-proteasome system and other hydrolytic systems for protein degradation, we asked whether increased membrane-skeleton fragments could be detected in older RBCs. Methods: Four different anti-spectrin antibodies and an antibody anti-ubiquitin conjugates were used to analyse, by Western blotting, fragments of spectrin and other proteins in RBCs of different age separated in density gradients and characterized for their protein 4.1a/4.1b ratio as a cell age parameter. Results: spectrin fragments do exist in RBCs of all ages, they represent a minute fraction of all spectrin, are membrane-bound and not cytoplasmic and do not increase with cell age. Besides spectrin, other membrane-skeletal components decrease with cell age. Conclusion: Observed results challenge the commonly accepted view that decrease in cell membrane throughout RBC life in vivo occurs via the release of spectrin-free vesicles.