Dopamine decreases Na-K ATPase (NKA) activity by PKC-dependent phosphorylation and endocytosis of the NKA alpha1. Dopamine-mediated regulation of NKA is impaired in aging and some forms of hypertension. Using opossum (OK) proximal tubule cells (PTCs), we demonstrated that sodium-hydrogen exchanger regulatory factor-1 (NHERF-1) associates with NKA alpha1 and dopamine-1 receptor (D1R). This association is required for the dopamine-mediated regulation of NKA. In OK cells dopamine decreases NHERF-1 association with NKA alpha1 but increases its association with D1R. However, it is not known whether NHERF-1 plays a role in dopamine-mediated NKA regulation in animal models of hypertension. We hypothesized that defective dopamine-mediated regulation of NKA results from the decrease in NHERF-1 expression in rat renal PTCs isolated from animal models of hypertension (SHRs and aged F344 rats). To test this hypothesis, we isolated and cultured renal PTCs from 22-mo old F344 rats and their controls, normotensive 4-mo old F344 rats, and spontaneously hypertensive rats (SHR) and their controls, normotensive Wistar-Kyoto (WKY) rats. The results demonstrate that in both hypertensive models (SHR and aged F344), NHERF1 expression, dopamine-mediated phosphorylation of NKA, and ouabain-inhibitable K+ transport are reduced. Transfection of NHERF-1 into PTCs from aged F344 and SHRs restored dopamine-mediated inhibition of NKA. These results suggest that decreased renal NHERF-1 expression contributes to the impaired dopamine-mediated inhibition of NKA in PTCs from animal models of hypertension.