Colocalization and coprecipitation of ankyrin and Na+,K+-ATPase in kidney epithelial cells

Interactions between integral proteins of the plasma membrane and the cytoskeleton may be important for localizing certain membrane proteins in a nonrandom fashion at specialized domains of the cell surface. Here, we show that ankyrin, the key protein for the linkage of the erythrocyte anion exchanger (band 3) to the spectrin-based membrane cytoskeleton, is also present in kidney distal tubular cells where ankyrin is precisely colocalized with Na+,K+-ATPase. Both proteins are confined to the basolateral plasma membrane and are absent from the apical membrane, the junctional complex and the membrane surface that contacts the basal lamina. Purified Na+,K+-ATPase of sheep and pig kidney contains a binding site for erythrocyte ankyrin as demonstrated by immunoprecipitation experiments. A band 3-like binding site for ankyrin is likely, since binding of ankyrin to Na+,K+-ATPase could be inhibited in a competitive fashion by the isolated cytoplasmic domain of erythrocyte band 3.