Excess of red cell membrane proteins in hereditary high-phosphatidylcholine hemolytic anemia

Abstract

Previous descriptions of hereditary high-phosphatidylcholine hemolytic anemia (HPCHA) have highlighted the association of increased erythrocyte membrane phosphatidylcholine with abnormal membrane cation permeability. We studied the function and composition of erythrocyte membranes from three individuals with HPCHA to characterize further the membrane abnormalities in this disorder. Despite significant macrocytosis, HPCHA red cells were dehydrated and showed an increased surface area to volume ratio compared to normal red cells. The passive efflux of K+ from HPCHA erythrocytes was increased fourfold at 37 degrees C. Total membrane phospholipid was increased 7-42%, largely due to excess phosphatidylcholine, which made up 35.8-37.2% of total phospholipid. Membrane cholesterol:phospholipid ratios were in the normal range. It appears that the excess phosphatidylcholine was not acquired during circulation, since plasma lipids were normal and all subpopulations of density-separated HPCHA erythrocytes were similarly abnormal. The ratio of total protein to phospholipid in white ghosts was increased, indicating that membrane protein was increased to an even greater extent than membrane lipids. No abnormal membrane proteins were identified by Coomassie or periodic acid Schiff (PAS) staining. Quantitation of the major membrane proteins indicated that the total protein excess in HPCHA membranes was due to a proportional increase in all major proteins. We conclude that HPCHA erythrocytes have excess membrane proteins and hypothesize that the changes in lipid composition and cation permeability are secondary to underlying protein abnormalities, which remain to be defined.