Molecular basis of antihypertensive effect of bradikinin: functional involvement of renal aquaporins.

Bradykinin (BK) is one of the most important peptide regulating vascular tone, water, and ionic balance in the body, playing a key role in controlling blood pressure. Interestingly, patients with essential hypertension excrete less BK than do normotensive subjects. To elucidate the mechanism by which BK regulates renal water transport, AQP2-transfected collecting duct CD8 cells, expressing the BK receptor (BK2), were used as experimental model. In CD8 cells, BK pretreatment impaired forskolin-induced AQP2 translocation to the apical plasma membrane. To clarify the signal transduction cascade associated with this effect, we first investigated whether BK induced increase in citosolic calcium, via the G protein Gq known to be coupled to BK2 receptor. Spectrofluorometry employing fura-2-AM revealed that 100 nM BK elicited a significant increase in Cai (from 72.8 ± 7.4, to 310.7 ± 43.4 nM, n=6, P which was abolished by the receptor antagonist HOE-140. In renal cells, Gq coupled receptors may activate Rho and its downstream effectors. In CD8 cells it has been shown that forskolin-induced AQP2 translocation is associated with a decrease in Rho activity and depolymerization of F-actin which facilitates the translocation of AQP2 to the plasma membrane. Interestingly, BK treatment in CD8 cells resulted in a significant increase in Rho activity, as assessed by selective pull down experiments. In agreement with these data, BK induced a significant increase of F-actin content as assessed by actin polymerization assay and by immunofluorescence experiments. BK effects on actin assembly were abolished by the BK2 agonist HOE-140. We conclude that the diuretic effect of bradykinin may in part be explained by impairement of AQP2 translocation via activation of Rho and F-actin formation. [ABSTRACT FROM AUTHOR]