RESUMO
Previous data showed that prostaglandin E2 (PGE2) mediates the inhibitory effect of bradykinin (BK) on proximal tubule (PT) Na+-ATPase activity. The aim of this work was to investigate the molecular mechanisms involved in the effect of PGE2 on PT Na+-ATPase. We used isolated basolateral membrane (BLM) from pig PT, which expresses several components of different signaling pathways. The inhibitory effect of PGE2 on PT Na+-ATPase activity involves G-protein and the activation of protein kinase A (PKA) because: (1) PGE2 increased [³5S]GTPγS binding; (2) GDPßS abolished the inhibitory effect of PGE2; (3) PGE2 increased PKA activity; (4) the inhibitory effect of PGE2 was abolished by PKA inhibitor peptide. We observed that the PKA-mediated inhibitory effect of PGE2 on PT Na+-ATPase activity requires previous activation of protein kinase C. In addition, we observed that PGE2 stimulates Ca²+-independent phospholipase A2 activity representing an important positive feedback to maintain the inhibition of the enzyme. These results open new perspectives to understanding the mechanism involved in the effect of PGE2 on proximal tubule sodium reabsorption.
