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Recently, we demonstrated that bradykinin (BK) counteracts the stimulatory effect of Ang-(1–7) on the Na+-ATPase activity from basolateral membrane of the proximal tubule through B2 receptor. In the present paper, the signaling pathway involved in the inhibitory response of the Na+-ATPase activity to BK was investigated. The following results indicate that the phospholipase A2 (PLA2)/COX/prostaglandin E (PGE2) pathway is implicated in this process: (1) The inhibitory effect of BK on Ang-(1–7)-stimulated enzyme is abolished in a dose-dependent manner by quinacrine (10−9;-10−6M), a nonspecific PLA2 inhibitor, and by PACOCF3 (10−7M), an inhibitor of a Ca2+-independent PLA2. However, AACOCF3 (2×10−4 M), an inhibitor of the cytosolic PLA2, does not modify the inhibitory effect of BK. (2) The inhibitory effect of BK on the Ang-(1–7)-stimulated enzyme is reversed by cyclooxygenase (COX) inhibitors diclofenac (10−12 M) and indomethacin (10−12 M). (3) PGE2 (10−12–10−5 M) inhibits the Na+-ATPase activity in a dose dependent manner. (4)The inhibitory effects of PGE2 and BK on the Na+-ATPase activity are not cumulative. (5) PGE2 (10−12–10−8 M) counteracts the stimulatory effect of Ang-(1–7) on the enzyme activity in a dose-dependent manner. [Copyright &y& Elsevier]

Recently, we demonstrated that angiotensin-(1–7) (Ang-(1–7)) stimulates the Na+-ATPase activity through a losartan-sensitive angiotensin receptor, whereas bradykinin inhibits the enzyme activity through the B2 receptor [Regul. Pept. 91 (2000) 45; Pharmacol. Rev. 32 (1980) 1]. In the present paper, the effect of bradykinin (BK) on Ang-(1–7)-stimulated Na+-ATPase activity was evaluated. Preincubation of Na+-ATPase with 10−9 M Ang-(1–7) increases enzyme activity from 7.9±0.9 to 14.1±1.5 nmol Pi mg−1 min−1, corresponding to an increase of 79% (p<0.05). This effect is reverted by bradykinin in a dose-dependent manner (10−14–10−8 M), reaching maximal inhibitory effect at 10−9 M. Des-Arg9 bradykinin (DABK), an agonist of B1 receptor, at the concentrations of 10−9–10−7 M, does not mimic the BK inhibitory effect, and des-Arg9-[Leu8]-BK (DALBK), a B1 receptor antagonist, at the concentrations of 10−10–10−7 M, does not prevent the inhibitory effect of BK on Ang-(1–7)-stimulated enzyme. On the other hand, HOE 140, an antagonist of B2 receptor, abolishes the inhibitory effect of BK on the Ang-(1–7)-stimulated enzyme in a dose-dependent manner, reaching maximal effect at 10−7 M. Taken together, these data indicate that stimulation of B2 receptors by BK can counteract the stimulatory effect of Ang-(1–7) on the proximal tubule Na+-ATPase activity. [Copyright &y& Elsevier]