Atrial natriuretic peptides and urodilatin modulate proximal tubule Na+-ATPase activity through activation of the NPR-A/cGMP/PKG pathway

The signaling pathway mediating modulation of Na+-ATPase of proximal tubule cells by atrial natriuretic peptides (ANP) and urodilatin through receptors located in luminal and basolateral membranes (BLM) is investigated. In isolated BLM, 10−11 M ANP or 10−11 M urodilatin inhibited the enzyme activity (50%). Immunodetection revealed the presence of NPR-A in BLM and LLC-PK1 cells. Both compounds increased protein kinase G (PKG) activity (80%) and this effect did not occur with 10−6 M LY83583, a specific inhibitor of guanylyl cyclase. The inhibitory effect of these peptides on Na+-ATPase activity did not occur after addition of 10−6 M KT5823, a specific inhibitor of PKG. LLC-PK1 cells were used to investigate if ANP and urodilatin change the activity of sodium pumps by luminal receptor interaction. ANP and urodilatin inhibited Na+-ATPase activity (50%), with maximal effect at 10−10 M, similar to 10−7 M db-cGMP, and did not occur with 10−7 M LY83583, a guanylyl cyclase inhibitor. ANP and urodilatin specifically inhibit Na+-ATPase activity by activation of the cGMP/PKG pathway through NPR-A located in luminal membrane and BLM, increasing understanding of the mechanism of natriuretic peptides on renal sodium excretion, with proximal tubule Na+-ATPase one possible target.