AbstractInflux of the K+analogue Rb+was measured through the ouabain‐sensitive Na+/K+pump and the ouabain‐insensitive “leak” pathways in Cl−or NO −3in mature red cells from adult pigs and in reticulocytes naturally occurring in 7‐day‐old piglets. In reticulocytes, Rb+influxes by the two pathways were of about equal magnitude in Cl−(13 and 10 mmoles/liter cells × hr) and at least 25‐fold larger than in mature red cells (0.5 and 0.4 mmoles/liter cells × hr). In Na+media, a portion of the ouabain‐insensitive “leak” flux of Rb+was Cl−dependent (Rb+Cl−transport) as NO −3replacement reduced Rb+influx by 90 in reticulocytes and by 40 in mature red cells. The sulfhydryl reagent N‐ethylmaleimide (NEM) stimulated Rb+Cl−transport about twofold in reticulocytes and up to 13‐fold in mature red cells. When reticulocytes matured to erythrocytes during in vitro incubation, about 90 of both ouabain‐sensitive Rb+pump and ouabain‐insensitive Rb+Cl−influx were lost. In contrast, the NEM‐stimulated Rb+Cl−transport changed much less throughout this period, suggesting an entity operationally but not necessarily structrually distinct from the basal Rb+Cl−transport. Although the experimental variability precluded a full assessment of significant changes in the small Na+/K+(Rb+) pump and Rb+Cl−fluxes in mature pig red cells kept for the same time period in vitro, Rb+flux changes in reticulocytes appear to be maturational in nature, reflecting parallel activity tra
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