ASSOCIATION OF INCREASED Na+-INFLU AND LACK OF AN INTEGRAL ERYTHROCYTE MEMBRANE PROTEIN N HEREDITARY STOMATO-CYTOSIS

Abstract

Hereditary stomatocytosis is a hemolytic anemia caused by an increased Na+ influx and consecutive hydrocytosis of the erythrocytes. In search of the pathogenesis, the erythrocyte membranes of two unrelated splenectomized patients suffering from severe stomatocytosis were analyzed by an analytical SDS polyacrylamid gradient gel electrophoresis. A diminution of the erythrocyte membrane protein band 7.2 (Mr ~ 28000) was detected. By separating the integral proteins in the outer plasma membrane (Low ionic strength extraction) from the peripheral proteins in the inner cytoskeleton (Triton X-100-extraction) we found that band 7.2 normally consists of two fractions. 50% represent a peripheral membrane protein (7.2a), while the other half is embedded in the lipid bilayer (7.2b). The investigation of the red cell cation fluxes showed, that the passive influx of Na+ was disproportionately increased (50-fold) compared to only a slightly enhanced passive efflux of K+ (5-fold). Inspite of an elevated total Na+ efflux, there is a net Na+ influx of 17.8 mval/l cells × hour. The heterozygous parents, who are clinically unaffected, compensate their 3-fold increase of passive Na+ influx by an increased total Na+ efflux. It is suggested that by the absence of band 7.2b an oligomeric complex of transmembrane proteins, responsible for the passive Na+ influx, may desintegrate and thereby allow an enhanced Na+ influx into the stomatocytic erythrocyte. The lack of band 7.2b, proven by SDS-polyacrylamidgel electrophoresis, should be a valuable diagnostic for hereditary stomatocytosis.