H⁺-ATPase Activity in Collecting Duct Segments in Protein-Deprived Rats – Role of Angiotensin II on Its Regulation

Background: Enhanced expression of the genes that encode for components of the renin-angiotensin system (RAS) has been exhibited in low-protein-fed (LP) rats. We examined distal proton secretion in LP rats through the activity of H⁺-ATPase on microdissected CCD, OMCD and IMCD segments. The effect of angiotensin II AT₁ receptor inhibition and protein recovery (24% protein) on H⁺-ATPase activity was studied. Methods: Bafilomycin-sensitive H⁺-ATPase activity on CCD, OMCD and IMCD segments of LP (protein 8%) and control rats CP (protein 24%) was evaluated. We examined the levels of mRNA expression of RAS components: angiotensin-converting enzyme (ACE), angiotensinogen and angiotensin II AT₁ expression; AT₁receptor binding and distribution were determined by quantitative autoradiography. Results: Increased ACE and AT₁ mRNA expression was found in cortex and medulla of LP compared to NP rats. AT₁ receptor binding density was significantly reduced in renal cortex and inner stripe of the outer medulla of LP compared to NP rats. Minimal radioligand binding was shown in inner medulla of LP. Whole kidney expression of angiotensinogen was unaltered in LP. H⁺-ATPase activity significantly decreased in IMCDs and OMCDs of LP. The inhibitory effect of LP was abolished when OMCD segments were incubated for 60 min in the presence of losartan 10–⁶ to 10–⁸M. There was no effect of losartan concentrations from 10–⁶ to 10–⁸ M on IMCDs. Similar results were observed on H⁺-ATPase activity in OMCD and IMCD segments after readministration of 24% protein in the diet. Conclusion: Both the recovery of H⁺-ATPase activity in OMCD segments induced by losartan and the increased expression of AT₁receptor suggest angiotensin II modulation of proton ATPase activity on this duct segments in LP rats. Intense compromise of proton secretion through the continued H⁺-ATPase inhibition in IMCDs from LP was shown.