RENAL NA+, K+-ATPASE IN DAHL SALT-SENSITIVE RATS - K+ DEPENDENCE, EFFECT OF CELL ENVIRONMENT AND PROTEIN-KINASES

Na+,K+-ATPase in renal epithelial cells plays an important role in the regulation of Na+ balance, extracellular volume and blood pressure. The function of renal Na+,K+-ATPase in Dahl salt-sensitive (DS) rats, an animal model for salt-sensitive hypertension, and Dahl salt-resistant (DR) rats has been studied. In Na+,K+-ATPase partially purified from renal cortex, affinities and the Hill coefficients for Na+ and K+ activation were similar in DS and DR rats. Only one component of low ouabain affinity site was found in both strains, indicating the presence of the alpha1 isoform. Protein kinase C and cAMP-dependent protein kinase phosphorylated Na+,K+-ATPase alpha subunit in DS and DR rats, and the phosphorylation by protein kinase C was associated with an inhibition of enzyme activity. The kinetic parameters for K+ activation were also studied in a preparation of basolateral membranes and were found to be similar in DS and DR rats. In a preparation of cortical tubule cells, Na+,K+-ATPase activity was determined as ouabain-sensitive oxygen consumption (OS QO2). Maximal OS QO2, measured in Na+ loaded cells, was the same in DS and DR rats. The K0.5 for K+ was significantly lower in DS than DR rats (0. 163 +/- 0.042 vs. 0.447 +/- 0.061 mm, P < 0.05), indicating that factors regulating Na+,K+-ATPase activity in intact cells are altered in DS rats. Kinetic parameters for Na+ activation in cells were the same in both strains. In summary, the function of renal Na+,K+-ATPase molecule is not altered in DS rats. The intracellular systems that regulate renal Na+,K+-ATPase activity might be different in DS and DR rats.