DISTRIBUTION OF DOPAMINE-DEPENDENT AND CAMP-DEPENDENT PHOSPHOPROTEIN (DARPP-32) IN THE DEVELOPING AND MATURE KIDNEY

DARPP-32 is a dopamine- and cAMP-regulated inhibitor of protein phosphatase-I (PP-1). Dopamine and DARPP-32 regulate sodium reabsorption in renal tubules by inhibiting the activity of Na+,K+-ATPase. We here report the pre- and postnatal distributions of DARPP-32 in the kidney as demonstrated by immunoblotting and immunohistochemistry. With immunoblotting we examined the abundance of DARPP-32 and the functionally similar but more widespread inhibitor of PP-1, inhibitor-1 (I-1). We compared their relative abundance in the renal cortex, renal medulla and neostriatum from the brain, where DARPP-32 is greatly enriched. DARPP-32 levels in the adult rat were fourfold higher in the neostriatum than in the renal medulla and 13-fold higher than in the renal cortex. I-1 levels were approximately the same in the neostriatum and in the renal medulla and 2.5-fold higher in neostriatum than in the renal cortex. Between postnatal day 10 (PN10) and 40 (PN40) DARPP-32 abundance increased 1.3-fold in the neostriatum, 1.4-fold in the renal cortex and sixfold in the medulla. The abundance of I-1 did not increase in the striatum from PN 10 to PN40 but increased 1. 5-fold in the renal cortex and threefold in the renal medulla. Thus, during the time of maturation of tubular transport function, the levels of both PP-1 inhibitors increased in the kidney, the largest increase being found in the renal medulla. With immunohistochemistry strong DARPP-32-like-immunoreactivity (DARPP-32-LI) was detected in the ureteral buds from gestational day 18 and up to postnatal day 8 when nephrogenesis was completed. No I-1-like immunoreactivity (I-1-LI) was found in the ureteral buds. From gestational day 21, DARPP-32-LI was identified in the proximal convoluted tubules. After postnatal day 8, DARPP-32-LI increased greatly in the medullary tubules of the thick ascending limb of Henle. These results suggest two separate roles for DARPP-32 in renal function. During tubulogenesis, DARPP-32 may participate in differentiation/proliferation. In the mature kidney, DARPP-32 participates in the regulation of sodium excretion.