Identification of a major locus contributing to erythrocyte 2,3-diphosphoglycerate variability in hooded (Long-Evans) rats.

The erythrocyte glycolytic intermediate 2,3-diphosphoglycerate (DPG) and adenosine triphosphate (ATP) play an important role in oxygen transport and delivery by binding to hemoglobin (Hb) and reducing its affinity for oxygen. Considerable quantitative variability in the levels of DPG and ATP exists in human populations and in a population of hooded (Long-Evans) rats we have studied. This paper presents the results of studies on the genetic component of DPG-level variation in an outbred population of hooded rats. Beginning with about 100 rats, a two-way selection experiment was initiated. Pairs of rats with the highest DPG levels were mated to produce a High-DPG rat strain and animals with the lowest DPG levels were mated to produce a Low-DPG strain. Mean DPG levels responded rapidly to selection and, from generation 3 on, the differences between strain means were highly significant. Ten High-DPG strain rats were intercrossed with 10 Low-DPG strain rats of generation 10 to produce an F1 generation in which the DPG levels were almost as high as those of High-DPG animals. This indicates partial dominance of High-DPG alleles. The F2 DPG-level distribution showed two distinct subpopulations. The high DPG subpopulation contained three times as many animals as the low DPG subpopulation. From these results and the statistical analyses performed, it was concluded that the DPG differences between strains were due to an allelic difference at one major locus, the allele carried by the High-DPG strain showing partial dominance over the allele carried by the Low-DPG strain. It appears that this locus may also effect ATP levels to a large extent and is polymorphic in hooded rat populations. Identification of this locus gives us a useful tool for studies of the physiological effects of DPG variability, as well as providing an example of a major gene effect in a quantitatively varying trait.