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

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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 < 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.