Loss of sodium-hydrogen exchanger regulatory factor-1 (NHERF-1) expression

36 Dopamine decreases Na-K ATPase (NKA) activity by PKC-dependent phosphorylation 37 and endocytosis of the NKA α1. Dopamine-mediated regulation of NKA is impaired in 38 aging and some forms of hypertension. Using opossum (OK) proximal tubule cells 39 (PTCs), we demonstrated that sodium-hydrogen exchanger regulatory factor-1 40 (NHERF-1) associates with NKA α1 and dopamine-1 receptor (D1R). This association is 41 required for the dopamine-mediated regulation of NKA. In OK cells dopamine decreases 42 NHERF-1 association with NKA α1 but increases its association with D1R. However, it 43 is not known whether NHERF-1 plays a role in dopamine-mediated NKA regulation in 44 animal models of hypertension. We hypothesized that defective dopamine-mediated 45 regulation of NKA results from the decrease in NHERF-1 expression in rat renal PTCs 46 isolated from animal models of hypertension (SHRs and aged F344 rats). To test this 47 hypothesis, we isolated and cultured renal PTCs from 22-mo old F344 rats and their 48 controls, normotensive 4-mo old F344 rats, and spontaneously hypertensive rats (SHR) 49 and their controls, normotensive Wistar-Kyoto (WKY) rats. The results demonstrate that 50 in both hypertensive models (SHR and aged F344), NHERF1 expression, dopamine51 mediated phosphorylation of NKA, and ouabain-inhibitable K transport are reduced. 52 Transfection of NHERF-1 into PTCs from aged F344 and SHRs restored dopamine53 mediated inhibition of NKA. These results suggest that decreased renal NHERF-1 54 expression contributes to the impaired dopamine-mediated inhibition of NKA in PTCs 55 from animal models of hypertension. 56 57