Physiological concentrations of angiotensin II (Ang II) (10-12 to 10-9) stimulate sodium reabsorption in the proximal tubule, which in turn affects blood pressure, and contributes to the development of hypertension. Our recent work shows that Ang II rapidly (≤ 2 min), directly, and robustly stimulates the activity of Na,K-ATPase, the active transport mechanism that ultimately drives sodium reabsorption. Under these
conditions Ang II also alters the phosphorylation and conformation of Na,K-ATPase. To test the role of phosphorylation in regulating pump activity we have co-expressed the rat α-subunit in opossum kidney cells, a proximal tubule cell line, along with AT1A receptor. In these cells Ang II stimulates the activity of the rat sodium proximal tubule. By doing site-directed mutagenesis we plan to test which sites of phosphorylation are responsible for the observed stimulation.