An abnormal handling of renal magnesium has been suggested to cause salt-sensitive hypertension, The filtered magnesium is first reabsorbed in the proximal tubule. Amiloride has been shown to enhance renal magnesium conservation, but the regulatory mechanisms are unknown yet. High-salt (8% NaCl) diet decreased serum magnesium concentration, while increased urinary magnesium in Dahl salt-sensitive (DS) rat. Furthermore, the expression of nitric oxide synthase type 3 and nitric oxide (NO) content were decreased in high-salt loaded DS rat. In isolated proximal tubule cells, amiloride (0.1 mM.) increased intracellular free magnesium concentration ([Mg2+](i)). However, the net [Mg2+](i) increase in the high-salt loaded DS rat was smaller than other groups. NOR1 (0.1 mM), a NO donor, restored the increase of [Mg2+](i) to the same level of other groups. On the contrary, L-NMMA (0.1 mM) an inhibitor of NO production, inhibited the increase of [Mg2+](i) in all groups. These results suggest that intracellular NO has an important role to up-regulate amiloride-elicited magnesium influx. (C) 2002 Elsevier Science (USA). All rights reserved.