The physiological roles of ANG-(3-4) (Val-Tyr), a potent ANG II-derived peptide, remain largely unknown. the present study 1) investigates whether ANG-(3-4) modulates ouabain-resistant Na+-ATPase resident in proximal tubule cells and 2) verifies whether its possible action on pumping activity, considered the fine tuner of Na+ reabsorption in this nephron segment, depends on blood pressure. ANG-(3-4) inhibited Na+-ATPase activity in membranes of spontaneously hypertensive rats (SHR) at nanomolar concentrations, with no effect in Wistar-Kyoto (WKY) rats or on Na+-K+-ATPase. PD123319 (10(-7) M) and PKA((5-24)) (10(-6) M), an AT(2) receptor (AT(2)R) antagonist and a specific PKA inhibitor, respectively, abrogated this inhibition, indicating that AT(2)R and PKA are central in this pathway. Despite the lack of effect of ANG-(3-4) when assayed alone in WKY rats, the peptide (10(-8) M) completely blocked stimulation of Na+-ATPase induced by 10(-10) M ANG II in normotensive rats through a mechanism that also involves AT(2)R and PKA. Tubular membranes from WKY rats had higher levels of AT(2)R/AT(1)R heterodimers, which remain associated in 10(-10) M ANG II and dissociate to a very low dimerization state upon addition of 10(-8) M ANG-(3-4). This lower level of heterodimers was that found in SHR, and heterodimers did not dissociate when the same concentration of ANG-(3-4) was present. Oral administration of ANG-(3-4) (50 mg/kg body mass) increased urinary Na+ concentration and urinary Na+ excretion with a simultaneous decrease in systolic arterial pressure in SHR, but not in WKY rats. Thus the influence of ANG-(3-4) on Na+ transport and its hypotensive action depend on receptor association and on blood pressure.Brazilian National Research CouncilFundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)National Institute of Science and Technology for Structural Biology and Bioimaging, BrazilBrazilian Federal Agency for Support and Evaluation of Graduate EducationUniv Fed Rio de Janeiro, Carlos Chagas Filho Inst Biophys, BR-21941902 Rio de Janeiro, BrazilNatl Inst Sci & Technol Struct Biol & Bioimaging, Rio de Janeiro, BrazilUniversidade Federal de São Paulo, Dept Biophys, São Paulo, BrazilUniv Fed Rio de Janeiro, Inst Biomed Sci, BR-21941902 Rio de Janeiro, BrazilUniversidade Federal de São Paulo, Dept Biophys, São Paulo, BrazilBrazilian National Research Council: 302513/2008-6FAPERJ: E-26/102.764/2008FAPERJ: E-26/103.050/2012FAPESP: 12/50475-2National Institute of Science and Technology for Structural Biology and Bioimaging, Brazil: 573767/2008-4Web of Scienc
