Renal dopamine DA(1) receptor coupling with G(s) and G(q/11) proteins in spontaneously hypertensive rats

The dopamine DA(1) receptor transduces its signal via adenylyl cyclase and phospholipase C in the renal proximal tubule, which has been suggested to be defective at the level of receptor-G protein coupling in spontaneously hypertensive rats (SHR). We prepared basolateral membranes from Wistar-Kyoto (WKY) rats and SHR to determine the coupling of DA(1) receptor with G proteins, especially G(q/11). Fenoldopam, a DA(1)-receptor agonist, produced a time- and concentration-dependent stimulation in S-35-labeled guanosine 5'-O-(3-thiotriphosphate) ([S-35]GTP gamma S) binding in WKY rats. Fenoldopam-induced (10 mu M) stimulation was significantly inhibited by a DA(1)-receptor antagonist, Sch-23390. Specific antibodies against COOH terminals of G(s) alpha and G(q/11)alpha produced 50-60% and 40-50% inhibition, respectively, in fenoldopam stimulation of [S-35]GTP gamma S binding. Western analysis of basolateral membranes with these antibodies revealed the presence of G(s) alpha (45 kDa) and G(q/11)alpha (42 kDa). Fenoldopam stimulation of [S-35]GTP gamma S binding was significantly attenuated in SHR compared with WKY rats. Parathyroid hormone stimulation of [S-35]GTP gamma S binding was similar in SHR and WKY rats, whereas stimulation by phenylephrine was significantly reduced in SHR. Densitometric quantification of 42-kDa band showed a reduced amount in SHR, whereas the density of 45-kDa band was not significantly different compared with WKY rats. We provide the direct evidence showing the coupling of DA(1) receptor with G(q/11)alpha and G(s) alpha and propose that, in addition to a defect in the receptor-G protein coupling, a reduced amount of G(q/11)alpha observed in the hypertensive animals may also contribute to the diminished dopamine-induced inhibition of Na+-K+-adenosinetriphosphatase in SHR.