Selective loss of calcium permeability on maturation of reticulocytes

Abstract

Calcium and sodium permeability of human reticulocytes have been studied and compared to mature erythrocytes. Mature erythrocytes had extremely low Ca2+ permeability which was less than 0.1% of values published for squid axon or HeLa cells. Calcium entry was markedly increased in reticulocyte rich suspensions and the uptake was linearly related to the percentage of reticulocytes present. The data suggest that reticulocytes are 43 fold more permeable to Ca2+ than mature cells although their Ca2+ concentration is not increased. Sodium influx into reticulocyte rich suspensions was also increased in direct proportion to the percent of reticulocytes present. Reticulocytes are 6 fold more permeable to Na+ than mature cells so the ratio of Ca2+:Na+ permeability falls by 7 fold as the reticulocyte changes to an erythrocyte. [3H]Ouabain binding was increased in reticulocyte rich cell suspensions and the correlation suggested a value of about 4,000 sites per reticulocyte compared with 362 ± 69 per mature cell. Maturation of the human reticulocyte produces disproportionate changes in cation permeability and in particular a selective loss of Ca2+ permeability.