Modulation of the (Na+Â +Â K+)ATPase activity by Angiotensin-(1-7) in MDCK cells

In the present paper the effect of Ang-(1-7) on the distal tubule (Na+ + K+)ATPase activity was evaluated by using MDCK cells as a model. Confluent cell monolayers were incubated with increasing concentrations of Ang-(1-7) for 30 min. Thereafter, the (Na+ + K+)ATPase activity was evaluated and a dose-dependent (from 10−12 to 10−7 M) inhibition was observed. The maximal inhibitory effect (54%) was reached at the concentration of 10−8 M. The inhibitory effect of Ang-(1-7) was not affected by the AT2 receptor selective antagonist PD123319 (from 10−10 to 10−7 M) but was blocked in a dose-dependent manner by the AT1 receptor selective antagonists losartan (10−10 M), candesartan (10−17 M), irbesartan (2 × 10−12 M) and telmisartan (2 × 10−16 M). The signaling pathway triggered by stimulation of the AT1 receptor was also investigated. The PI-phospholipase C (PI-PLC) inhibitor U73122 (5 × 10−8 M) blocked the inhibitory effect elicited by Ang-(1-7). Involvement of the protein kinase C (PKC) was evidenced by the sensitivity of the inhibitory effect of Ang-(1-7) to calphostin C (6.32 × 10−7 M) and the lack of additive effects when the cells were co-incubated with Ang-(1-7) and 3.2 × 10−8 M PMA. Altogether, these results demonstrate that Ang-(1-7) inhibits the (Na+ + K+)ATPase activity of the prototypic distal tubule cell MDCK through the AT1 receptor-mediated stimulation of PI-PLC/PKC signaling pathway.