Differential regulation of Na+,K+-ATPase and the Na+-coupled glucose transporter in hypertensive rat kidney

Several Na+ transporters are functionally abnormal in the hypertensive rat. Here, we examined the effects of a high-salt load on renal Na+,K+-ATPase a nd the sodium-coupled glucose transporter (SGLT1) in Dahl salt-resistant (D R) and salt-sensitive (DS) rats. The protein levels of Na+,K+-ATPase and SG LT1 in the DS rat were the same as those in the DR rat, and were not affect ed by the high-salt load. In the DS rat, a high-salt load decreased Na+,K+- ATPase activity, and this decrease coincided with a decrease in the apparen t Mechaelis constant (K-m) for ATP, but not with a change of maximum veloci ty(V-max). On the contrary, a high-salt load increased SGLT1 activity in th e DS rat, which coincided with an increase in the V-max for alpha -methyl g lucopyranoside. The protein level of phosphorylated tyrosine residues in Na +,K+-ATPase was decreased by the high-salt load in the DS rat. The amount o f phosphorylated serine was not affected by the high-salt load in DR rats, and could not be detected in DS rats. On the other hand, the amount of phos phorylated serine residues in SGLT1 was increased by the high-salt load. Ho wever, the phosphorylated tyrosine was the same for all samples. Therefore, we concluded that the high-salt load changes the protein kinase levels in DS rats, and that the regulation of Na+,K+-ATPase and SGLT1 activity occurs via protein phosphorylation. (C) 2001 Elsevier Science B.V. All rights res erved.