The Synergistic Roles of Cholecystokinin B and Dopamine D ₅ Receptors on the Regulation of Renal Sodium Excretion

Abstract

Renal dopamine D ₁-like receptors (D ₁R and D ₅R) and the gastrin receptor (CCK _BR) are involved in the maintenance of sodium homeostasis. The D ₁R has been found to interact synergistically with CCK _BR in renal proximal tubule (RPT) cells to promote natriuresis and diuresis. D ₅R, which has a higher affinity for dopamine than D ₁R, has some constitutive activity. Hence, we sought to investigate the interaction between D ₅R and CCK _BR in the regulation of renal sodium excretion. In present study, we found D ₅R and CCK _BR increase each other’s expression in a concentration- and time-dependent manner in the HK-2 cell, the specificity of which was verified in HEK293 cells heterologously expressing both human D ₅R and CCK _BR and in RPT cells from a male normotensive human. The specificity of D ₅R in the D ₅R and CCK _BR interaction was verified further using a selective D ₅R antagonist, LE-PM436. Also, D ₅R and CCK _BR colocalize and co-immunoprecipitate in BALB/c mouse RPTs and human RPT cells. CCK _BR protein expression in plasma membrane-enriched fractions of renal cortex (PMFs) is greater in D ₅R ^-/- mice than D ₅R ^+/+ littermates and D ₅R protein expression in PMFs is also greater in CCK _BR ^-/- mice than CCK _BR ^+/+ littermates. High salt diet, relative to normal salt diet, increased the expression of CCK _BR and D ₅R proteins in PMFs. Disruption of CCK _BR in mice caused hypertension and decreased sodium excretion. The natriuresis in salt-loaded BALB/c mice was decreased by YF476, a CCK _BR antagonist and Sch23390, a D ₁R/D ₅R antagonist. Furthermore, the natriuresis caused by gastrin was blocked by Sch23390 while the natriuresis caused by fenoldopam, a D ₁R/D ₅R agonist, was blocked by YF476. Taken together, our findings indicate that CCK _BR and D ₅R synergistically interact in the kidney, which may contribute to the maintenance of normal sodium balance following an increase in sodium intake.