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

Abstract

ANG-(3–4) inhibits renal Na-ATPase in hypertensive rats through a mechanism that involves dissociation of ANG II receptors, heterodimers, and PKA. Am J Physiol Renal Physiol 306: F855–F863, 2014. First published February 12, 2014; doi:10.1152/ajprenal.00488.2013.—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 WistarKyoto (WKY) rats or on Na-K-ATPase. PD123319 (107 M) and PKA(5–24) (106 M), an AT2 receptor (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 (108 M) completely blocked stimulation of Na-ATPase induced by 1010 M 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 1010 M ANG II and dissociate to a very low dimerization state upon addition of 108 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.