Inhibition of Na-K-ATPase in thick ascending limbs by NO depends on O2- and is diminished by a high-salt diet

• Published in: American journal of physiology. Renal physiology Vol. 56; no. 2; p. F224
• Main Authors: Varela, Marisela, Herrera, Marcela, Garvin, Jeffrey
• Format: Journal Article
• Language: English
• Published: Bethesda American Physiological Society 01.08.2004
• Subjects: Diet; Hypertension; Nitric oxide; Salt
• ISSN: 1931-857X; 1522-1466

A high-salt diet enhances nitric oxide (NO)-induced inhibition of transport in the thick ascending limb (THAL). Long exposures to NO inhibit Na-K-ATPase in cultured cells. We hypothesized that NO inhibits THAL Na-K-ATPase after long exposures and a high-salt diet would augment this effect. Rats drank either tap water or 1% NaCl for 7-10 days. Na-K-ATPase activity was assessed by measuring ouabain-sensitive ATP hydrolysis by THAL suspensions. After 2 h, spermine NONOate (SPM; 5 micro M) reduced Na-K-ATPase activity from 0.44 +/- 0.03 to 0.30 +/- 0.04 nmol Pi x micro g protein-1 x min-1 in THALs from rats on a normal diet (P < 0.03). Nitroglycerin also reduced Na-K-ATPase activity (P < 0.04). After 20 min, SPM had no effect (change -0.07 +/- 0.05 nmol Pi x micro g protein-1 x min-1). When rats were fed high salt, SPM did not inhibit Na-K-ATPase after 120 min. To investigate whether ONOO- formed by NO reacting with O2- was involved, we measured O2- production. THALs from rats on normal and high salt produced 35.8 +/- 0.3 and 23.7 +/- 0.8 nmol O2- x min-1 x mg protein-1, respectively (P < 0.01). Because O2- production differed, we studied the effects of the O2- scavenger tempol. In the presence of 50 micro M tempol, SPM did not inhibit Na-K-ATPase after 120 min (0.50 +/- 0.05 vs. 0.52 +/- 0.07 nmol Pi x micro g protein-1 x min-1). Propyl gallate, another O2- scavenger, also prevented SPM-induced inhibition of Na-K-ATPase activity. SPM inhibited pump activity in tubules from rats on high salt when O2- levels were increased with xanthine oxidase and hypoxanthine. We concluded that NO inhibits Na-K-ATPase after long exposures when rats are on a normal diet and this inhibition depends on O2-. NO donors do not inhibit Na-K-ATPase in THALs from rats on high salt due to decreased O2- production. [PUBLICATION ABSTRACT]