Impaired Stimulatory Effect of ETB Receptor on D3 Receptor in Immortalized Renal Proximal Tubule Cells of Spontaneously Hypertensive Rats

Abstract

Background: Activation of renal D₃ receptor induces natriuresis and diuresis in Wistar-Kyoto (WKY) rats; in the presence of ETB receptor antagonist, the natriuretic effect of D₃ receptor in WKY rats is reduced. We hypothesize that ETB receptor activation may regulate D₃ receptor expression in renal proximal tubule (RPT) cells from WKY rats, which is impaired in RPT cells from spontaneously hypertensive rats (SHRs). Methods: D₃ receptor expression was determined by immunoblotting; the D₃/ETB receptor linkage was checked by coimmunoprecipitation; Na⁺-K⁺-ATPase activity was determined as the rate of inorganic phosphate released in the presence or absence of ouabain. Results: In RPT cells from WKY rats, the ETB receptor agonist BQ3020 increased D₃ receptor protein. In contrast, in RPT cells from SHRs, BQ3020 did not increase D₃ receptor. There was coimmunoprecipitation between D₃ and ETB receptors in RPT cells from WKY and SHRs. Activation of ETB receptor increased D₃/ETB coimmunoprecipitation in RPT cells from WKY rats, but not from SHRs. The basal levels of D₃/ETB receptor coimmunoprecipitation were greater in RPT cells from WKY rats than in those from SHRs. Stimulation of D₃ receptor inhibited Na⁺-K⁺-ATPase activity, which was augmented by the pretreatment with the ETB receptor agonist BQ3020 in WKY RPT cells, but not in SHR RPT cells. Conclusion: ETB receptors regulate and physically interact with D₃ receptors differently in WKY rats and SHRs. The impaired natriuretic effect in SHRs may be, in part, related to impaired ETB and D₃ receptor interactions.