Fig. 4.

D1 receptor numbers and D1 receptor proteins in the membranes of proximal tubular epithelial cells of adult and old F344 rats. A: D1 receptor numbers were determined using 20 nM of radioactive D1 receptor-specific antagonist [³H]SCH-23390. B: D1 receptor proteins were measured by Western blot analysis using specific D1 receptor antibody. Bars are results as means ± SE (n = 4 cultures from 4 different rats). B: top right, immunoblot of D1 receptor proteins (lanes 1, 2, 5, 6: cultures from adult F344 rats; lanes 3, 4, 7, 8: cultures from old F344 rats); left, a positive control for D1 receptors in brain striatum of Sprague-Dawley rats (lane 1, 5 μg protein; lane 2, 15 μg protein).