Age-dependent changes in cation transport in the chicken erythrocyte

Previous work has shown that the transport phenotype of chicken erythrocytes changes with the age of the chicken. Here, we report changes in the transport of choline and K+ in erythrocytes from chickens at different developmental ages. The transport of choline in chicken erythrocytes was predominantly via saturable transport systems, was highest in erythrocytes from 1-day-old chickens and declined with chicken age when tested at 2 weeks of age and in mature chickens. Both Km and Vmax values for choline transport in chicken erythrocytes declined with chicken age. Similarly, the total unidirectional influx of K+ was highest in erythrocytes from 1-day-old chickens and declined with chicken age, as did ouabain-sensitive K+ influxes, which can be attributed to the Na+/K+ pump. In isotonic conditions, bumetanide-sensitive K+ influxes, which can be attributed to the Na+-K+-2Cl- cotransporter, were only measurable in erythrocytes from 1-day-old chickens. However, when stimulated by hypertonic conditions, bumetanide-sensitive K+ influxes were essentially identical in erythrocytes from 1-day- and 2-week-old chickens but decreased in erythrocytes from mature chickens. We conclude that both choline and K+ influxes decrease significantly in erythrocytes from chickens with increasing age. The changes are substantial but complex and may involve both regulation of existing transporters, and substitution or deletion of specific transporter isoforms.