Sodium-lithium countertransport activity is linked to chromosome 5 in baboons

The genes involved in the regulation of cellular sodium transport character istics, which are correlated with some forms of essential hypertension, hav e not yet been identified. We are studying the genes and environmental fact ors that affect red blood cell sodium-lithium countertransport (SLC) activi ty and intracellular sodium (ICNa) concentration in 634 baboons that compri se 11 pedigrees of 2 and 3 generations each. To detect and locate possible quantitative trait loci (QTLs) that affect SLC activity and ICNa concentrat ion, we performed a genome screen by using a maximum likelihood-based varia nce-components linkage analysis program (SOLAR). SLC and ICNa phenotypes as well as genotypes on 281 microsatellite loci were available for all pedigr eed animals. Both SLC and ICNa traits were highly heritable (residual herit ability 0.593 +/- 0.083 [P<0.0001] and 0.739+/-0.082 [P<0.0001], respective ly). We obtained evidence that a possible QTL for SLC activity is located o n the baboon homologue of human chromosome 4 between D4S2456 and D4S2365 wi th a maximum multipoint lod score of 9.3 (P<10(-10)) near D4S1645. This QTL accounts for approximately two thirds of the total additive genetic variat ion in SLC activity in baboons. Although ICNa concentration was highly heri table, we found no evidence for linkage to a QTL with use of this methodolo gy. Thus, we have evidence that a gene located on the baboon homologue of h uman chromosome 3 (baboon chromosome 5) affects cell sodium transport in ba boons.