Pig reticulocytes. V. Development of Rb+ influx during in vitro maturation

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Abstract
Influx of the K+ analogue Rb+ was measured through the ouabain-sensitive Na+/K+ pump and the ouabain-insensitive “leak” pathways in Cl− or NO in 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 replacement 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 transitions of Na+/K+ pump and Cl−-dependent K+ fluxes in vivo.