ANG-(3–4) inhibits renal Na+-ATPase in hypertensive rats through a mechanism that involves dissociation of ANG II receptors, heterodimers, and PKA

Abstract

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 (10−7M) and PKA(5–24)(10−6M), an AT2receptor (AT2R) antagonist and a specific PKA inhibitor, respectively, abrogated this inhibition, indicating that AT2R and PKA are central in this pathway. Despite the lack of effect of ANG-(3–4) when assayed alone in WKY rats, the peptide (10−8M) completely blocked stimulation of Na+-ATPase induced by 10−10M ANG II in normotensive rats through a mechanism that also involves AT2R and PKA. Tubular membranes from WKY rats had higher levels of AT2R/AT1R heterodimers, which remain associated in 10−10M ANG II and dissociate to a very low dimerization state upon addition of 10−8M 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.