Glomerular and Tubular α- and α-Adrenoceptors in the Rat Kidney

Abstract

Rat kidney glomeruli and cortical tubules were obtained by a combination of sieving and differential centrifugation technique. [3H]Prazosin and [3H]rauwolscine were used to identify and quantify the alpha 1- and alpha 2-adrenergic receptors, respectively. In the glomeruli, the alpha 1-adrenoceptor concentration was 27% and alpha 2-adrenoceptor concentration was 33% of the corresponding values in the tubules. Further localization of the tubular alpha-adrenoceptors was undertaken by studies in the isolated basolateral membrane and comparison with values in the crude plasma membrane. alpha 1-Adrenoceptors were enriched 1.54 +/- 0.1 times and alpha 2-adrenoceptors were enriched 1.73 +/- 0.04 times in the basolateral membrane as compared to crude plasma membrane. However, these values were significantly (p less than 0.05) less than the enrichment value of 2.77 +/- 0.3 obtained for the basolateral membrane marker (Na+ + K+)-ATPase. These results suggested the possibility that alpha 1- and alpha 2-adrenoceptors may also be distributed in the brush border membrane. Direct-binding studies in the purified renal brush border membrane indicated alpha 1-adrenoceptor concentration of 82.1 +/- 3.8 and alpha 2-adrenoceptor concentration of 108.2 +/- 9.3 fmol/mg protein. These values were 32 and 17% of the corresponding values in the basolateral membrane. Overall, our results suggest that alpha 1- and alpha 2-adrenoceptors are present both in the basolateral and brush border membranes analogous to what has been reported for angiotensin and insulin receptors; their primary concentration, however, is in the basolateral membranes.