Signaling through both angiotensin AT1 receptors (AT1R) and dopamine D1 receptors (D1R) modulates renal sodium excretion and arterial BP. AT1R and D1R form heterodimers, but whether treatment with AT1R antagonists functionally modifies D1R via allosterism is unknown. In this study, the AT1R antagonist losartan strengthened the interaction between AT1R and D1R and increased expression of D1R on the plasma membrane in vitro. In rat proximal tubule cells that express endogenous AT1R and D1R, losartan increased cAMP generation. Losartan increased cAMP in HEK 293a cells transfected with both AT1R and D1R, but it did not increase cAMP in cells transfected with either receptor alone, suggesting that losartan induces D1R activation. Furthermore, losartan did not increase cAMP in HEK 293a cells expressing AT1R and mutant S397/S398A D1R, which disrupts the physical interaction between AT1R and D1R. In vivo, administration of a D1R antagonist significantly attenuated the antihypertensive effect of losartan in rats with renal hypertension. Taken together, these data imply that losartan might exert its antihypertensive effect both by inhibiting AT1R signaling and by enhancing D1R signaling. 23: 421-428, 201223: 421-428, . doi: 10.1681 Sodium excretion and renal vascular tonus are bidirectionally regulated by dopamine, acting on dopamine D1 receptors (D1R) and angiotensin II, acting on angiotensin AT1 receptors (AT1R). [1][2][3] Several lines of evidence suggest that AT1R and D1R form a heteromeric signaling complex. [4][5][6] We recently reported that activation of either AT1R or D1R might cause internalization and/or interruption of the signaling capacity of the other receptor. 6 These observations imply that AT1R and D1R may allosterically modulate each other. Several recent studies have shown that the G-protein coupled receptor (GPCR) often forms heteromers and it has been suggested that allosteric modification within such heteromers will fine-tune receptor signal strength and offer novel opportunities for therapeutic approaches. 7-10 Because AT1R antagonists are far more commonly used therapeutically than AT1R agonists, we decided to test whether losartan, an AT1R antagonist, 11 might influence AT1R and D1R interaction and modulate D1R signaling. Losartan has been widely used to lower arterial BP and to prevent or attenuate the progression of renal disease. [12][13][14][15] Notably, the losartan binding site in AT1R does not overlap with the angiotensin binding site. 16,17 This study was performed on rat renal proximal tubule cells (RPTCs) in primary culture and on HEK 293a (HEK) cells, a cell line derived from human embryonic kidney. The endogenous expressions of D1R and AT1R are relatively high in RPTCs 1,18 and low in HEK cells. Therefore, HEK cells were used for expression of fluorescently tagged receptors and J Am Soc Nephrol 421BASIC RESEARCH mutant receptors. We performed a series of biochemical studies, which indicated that losartan strengthens the interaction between AT1R and D1R and that losartan incr...

We conclude that prolactin is a natriuretic hormone which interacts with the renal dopamine system for its effects. The natriuretic response is associated with inhibition of proximal tubular Na(+), K(+)-ATPase activity.

Prolactin is a natriuretic hormone and acts by inhibiting the activity of renal tubular Na(+)-K(+)-ATPase activity. These effects require an intact renal dopamine system. Here, we have studied by which mechanism prolactin and dopamine interact in Sprague-Dawley rat renal tissue. Na(+)-K(+)-ATPase activity was measured as ouabain-sensitive ATP hydrolysis in microdissected renal proximal tubular segments. Intracellular signaling pathways were studied by a variety of different techniques, including Western blotting using phosphospecific antibodies, immunoprecipitation, and biotinylation assays. We found that dopamine and prolactin regulated Na(+)-K(+)-ATPase activity via similar signaling pathways, including protein kinase A, protein kinase C, and phosphoinositide 3-kinase activation. The cross talk between prolactin and dopamine 1-like receptors was explained by a heterologous recruitment of dopamine 1-like receptors to the plasma membrane in renal proximal tubular cells. Prolactin had no effect on Na(+)-K(+)-ATPase activity in spontaneously hypertensive rats, a rat strain with a blunted response to dopamine. These results further emphasize the central role of the renal dopamine system in the interactive regulation of renal tubular salt balance.