Age-related reduction in the number of rabbit erythrocyte Na, K-ATPase

The number of Na, K-ATPase units, assessed by [3H]-ouabain binding assay, was significantly less in erythrocytes from 17 mature (30-week) rabbits than in those from 17 young (16-week) ones (0.179 +/- 0.010 vs. 0.263 +/- 0.014 pmol/10(9) cells, p less than 0.01). Consistent with this finding, the erythrocyte sodium concentration was significantly higher in mature rabbits as compared with young animals (17.1 +/- 1.30 vs. 10.8 +/- 0.68 mmol/liter, p less than 0.01). When the assays were repeated in 8 of the young rabbits 8 weeks after the initial determination, both variables were found to be similar to the levels from mature animals. The data suggest that the activity of erythrocyte sodium pump declines with aging or growth of donor rabbits, as a result of a reduction in the number of Na, K-ATPase units.