Expression of the Dopamine D 3 Receptor Protein in the Rat Kidney

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Abstract
—The dopamine D 3 receptor subtype was identified in rat kidney using both light microscopic immunohistochemistry and electron microscopic immunocytochemistry. Antipeptide polyclonal antisera were directed to both extracellular and intracellular regions of the native D 3 receptor. Selectivity of the antipeptide antisera was validated by their ability to recognize native receptor protein expressed in permanently transfected mouse LTK − cells or Spodoptera fragiperda (Sf9) cell membranes. Light microscopic immunohistochemical staining for the D 3 receptor was observed only in the cortex. Specific staining was present in proximal and distal tubules, cortical collecting ducts, glomeruli, and renal vasculature. Immunostaining was observed predominantly in the apical portion of both the proximal and distal tubules. Renal arterial staining was prominent in the medial and adventitial layers. Electron microscopic immunocytochemistry revealed immunogold particles in arteriolar smooth muscle cells of the renal vasculature. In proximal and distal tubules and cortical collecting duct, immunogold staining was localized to apical portions of tubule cells. D 3 receptor immunogold staining in the glomeruli was clearly present in podocytes. Western blot analysis demonstrated a single D 3 receptor band in infected Sf9 cell membranes, in transfected LTK − cells, and in kidney and brain but not in noninfected Sf9 cell membranes or in D 2 or D 3 receptor transfected or nontransfected LTK − cells. The use of receptor subtype–selective antibodies allows for the tissue localization of specific dopamine receptors that are not distinguished by current pharmacological or ligand-binding technology. The rat kidney expresses the D 3 receptor at sites previously deemed to have D 2 -like receptors.