Autoradiographic localization of dopamine DA1 receptors in rat kidney with [3H]Sch 23390.

Dopamine receptors in the rat kidney were characterized by homogenate binding and in vitro autoradiography using the dopamine 1 (DA1)-selective antagonist [3H]Sch 23390. [3H]Sch 23390 binding in cortical membrane preparations was saturable, stereoselective, and competed for by DA agonists and antagonists with a rank order of potency consistent with the labeling of the DA1 receptor. [3H]Sch 22390 binding was best fit to a two-site model: a high affinity-low density site (KD1 4.9 +/- 1.4 nM, Bmax 1 31.4 +/- 13.8 fmol/mg protein) and a low affinity-high density site (KD2 86.4 +/- 23.9 nM, Bmax 2 848.0 +/- 227.4 fmol/mg protein). In vitro autoradiography indicated that [3H]Sch 22390 binding sites were restricted to the cortex. High-resolution autoradiography further indicated that [3H]Sch 22390 binding sites were localized primarily on proximal tubules. Glomeruli and other vascular elements were devoid of [3H]Sch 23390 binding sites. These results suggest that DA and DA1 agonists may affect sodium excretion by a direct action on proximal tubule sodium reabsorption.