Historical View and Some Unsolved Problems in Red Blood Cell Membrane Research

The article provides a comprehensive overview of biological membrane lipid composition and distribution and ion transport processes, focusing particularly on red blood cells (RBCs). It begins with a historical perspective, detailing the introduction of the terms 'cell' and 'membrane' in biological sciences, and the development of the fluid-mosaic model of membrane structure. Early findings on ion transport highlighted the non-equilibrium distribution of Na⁺ and K⁺ across cell membranes, leading to the discovery of the Na⁺/K⁺ pump. The article delves into the lipid composition of RBC membranes, emphasising the roles of various lipids, including cardiolipin, and the concept of lipid rafts. These rafts, enriched with sphingolipids and cholesterol, play crucial roles in cellular processes. Variations in RBC shapes are discussed, with biophysical theories explaining transformations and pathological conditions affecting RBC morphology, such as sickle cell anaemia. Na⁺ and K⁺ transporters in RBC membranes are explored, highlighting the almost ubiquitous presence of the Na⁺/K⁺ pump (absent in Carnivora RBCs) and various ion channels, including the Gárdos and Piezo1 channels. The article notes species-specific differences in ion transport mechanisms and the activation or suppression of transporters during RBC maturation. The mechanism of residual ion transport is examined, questioning whether a Na⁺(K⁺)/H⁺ antiporter exists in the human RBC membrane. Residual ion fluxes are mediated by this antiporter, influenced by the fatty acid composition of the RBC membrane. The outlook section underscores the need for further research to fully understand the complexities of RBC membrane structure and function, suggesting that many questions remain unanswered despite significant advances.