The cellular localization of DARPP-32, a dopamine-and cAMP-regulated phosphoprotein of Mr 32,000 that appears to mediate certain actions of dopamine in the mammalian brain by acting as an inhibitor of protein phosphatase 1, was studied in the kidney of several species. DARPP-32 mRNA and DARPP-32-like inmunoreactivity were found in the cytoplasm of cells in the thick ascending limb of the loop of Henle. The specific dopamine DA, agonist SKF 82526 caused a dose-dependent inhibition ofNa+,K+-ATPase activity, which could be blocked by SCH 23390, a specific DA, antagonist, and by PKI-(5-24) amide, a specific inhibitor of cAMP-dependent protein kinase. The results indicate that DA1 dopamine receptors and DARPP-32, an intracellular third messenger for dopamine, are part of the signal-transduction process for dopamine acting on renal tubule cells.The neurotransmitter dopamine may play an important role in control of renal function. Dopamine is synthesized within the kidney (1) and acts locally to produce natriuresis (2-5) and vasodilation (6). Although these roles for dopamine in kidney physiology are well established, the cellular localization of renal dopamine receptors has not been defined.DARPP-32, a dopamine-and cAMP-regulated phosphoprotein with an apparent molecular weight of 32,000 by SDS/PAGE, has been purified from cytosol of bovine caudate nucleus (7,8). The complete amino acid sequence of bovine brain DARPP-32 has been determined (9), and its cDNA has been isolated and sequenced (10). In the central nervous system, DARPP-32 has been shown to be localized to dopaminoceptive cells containing the D1 dopamine receptor (11,12). It appears to serve as an intracellular third messenger mediating the actions of dopamine at these receptors (7,8,(11)(12)(13). Thus, the phosphorylation of DARPP-32 in intact nerve cells is increased by dopamine acting on D1 receptors, stimulation of adenylate cyclase, formation of cAMP, and stimulation of cAMP-dependent protein kinase (7,8). DARPP-32, in its phosphorylated form, is a potent inhibitor of phosphoprotein phosphatase 1 (14) and has amino acid sequence homology with phosphatase inhibitor 1 (I-1), also an inhibitor of phosphatase 1 (9).DARPP-32 has been analyzed primarily in the central nervous system. However, DARPP-32-like immunoreactivity has been detected in brown fat cells in pig (15), and the protein has been identified and purified from bovine adipose tissue (16). Previous studies have also identified DARPP-32 in ciliary epithelium (17) and in adrenal chromaffin cells, parathyroid cells, and choroid plexus (13). Evidence has been obtained for the presence of D1-like receptors in several of these tissues (18)(19)(20)(21)(22). Thus, DARPP-32 appears to be a useful marker for cells containing the central (D1) and peripheral (DA1) dopamine receptors. In the present study we investigated the cellular localization of DARPP-32 and, for purposes of comparison, I-1, in the kidney. Both proteins were localized in the same cells of a specific portion of the loop of Henle; ...