LOCALIZATION AND QUANTIFICATION OF THE CYTOSKELETON-ASSOCIATED PROTEIN ADDUCIN IN THE KIDNEYS OF NORMAL AND MILAN HYPERTENSIVE RATS

Hypertension and kidney dysfunction in sodium transport observed in th e Milan hypertensive strain (MHS) of rats are genetically associated w ith point mutations of adducin, an actin-and spectrin-binding protein of the membrane cytoskeleton. Polymorphism in the adducin locus has be en reported to occur also in cases of human primary hypertension. In t his study we show by immunostaining that adducin is localized along th e basolateral epithelial membrane surface of the entire proximal and d istal tubule with no detectable differences between MHS rats and the n ormotensive control strain (MNS). However, the total amount of adducin in kidney homogenates is reduced by about 45% in MHS rats as determin ed by quantitative immunoblotting. In erythrocyte membranes of MHS rat s, adducin is reduced approximately 10%. The reduction of renal adduci n in MHS rats is mainly caused by a reduction of the adducin pool that is loosely associated with kidney membranes and can be released by th e non-ionic detergent, Triton X-100. The Triton-resistant, tightly mem brane-bound pool of renal adducin differed by approximately 10% betwee n MHS and MNS rats. Since several ion transporters have been shown to be tethered to the membrane cytoskeleton, we suppose that the reductio n of the dynamic, loosely bound pool of adducin in MHS rats might inte rfere with the normal turnover and incorporation of yet unknown transp orters involved in kidney sodium transport. However, the Na+,K+-ATPase appears to be not involved, as indicated by normal distribution and a mounts of NA(+),K+-ATPase in the kidney of MHS rats revealed by immuno staining and immunoblotting.