Direct evidence for chloride-dependent volume reduction in macrocytic sheep reticulocytes

Cytometric analysis of the volume-distribution of macrocytic reticulocytes from 6-8 days acutely anemic sheep of both high and low potassium erythrocyte type revealed hyposmotically induced cell volume reduction in K-free NaCl but not in Na-methane sulfonate (CH3SO3Na) media. Furthermore N-ethylmaleimide, known to stimulate K:Cl efflux in these cells, and low extracellular pH caused cell shrinkage in isosmotic NaCl but not in CH3SO3Na. These data suggest that cell volume reduction, physiologically occurring during reticulocyte maturation, is a Cl-dependent process most likely involving electro-neutral K:Cl transport known to exist in reticulocytes of both sheep cation genotypes.