title: Regulation of Na+/K+-ATPase activity by nitric oxide in the kidney and gill of the brown trout (Salmo trutta).
abstract: In teleost fish, successful osmoregulation involves controlled ion transport mechanisms in kidney and gill epithelia. In this study, the effect of nitric oxide (NO) on Na(+)/K(+)-ATPase was investigated in vitro in these two tissues in brown trout (Salmo trutta) acclimated to freshwater. The NO donor sodium nitroprusside (SNP) inhibited in situ Na(+)/K(+)-ATPase activity, measured as ouabain-sensitive Rb(+) uptake, in both samples of kidney and gill tissue and in isolated gill cells. The effect was dose-dependent in both tissues, with a maximal observed inhibition of approximately 40-50% (1 mmol l (-1) SNP). The time-course of inhibition revealed a maximum effect with 10 min pre-incubation. The effect of SNP was reproduced with another NO donor, papa-nonoate (NOC-15; 200 micro mol l(-1)), and was prevented by the NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO; 1 mmol l(-1)). To further investigate the mechanism of the NO effect, whole-tissue Na(+) and K(+) levels were analysed. In kidney, SNP (1 mmol l(-1)) led to an increase in tissue Na(+) levels and a decrease in K(+) levels in a 3:2 ratio. In gill tissue, no change in either ion was observed. These observations indicate that the effect on Na(+)/K(+)-ATPase is direct rather than due to a decrease in intracellular Na(+), its rate-limiting substrate. SNP elevated the level of cyclic GMP (cGMP) in both kidney and gill tissue. Dibutyryl cyclic GMP (db-cGMP; 1 mmol l(-1)) also inhibited Na(+)/K(+)-ATPase activity in both tissues. Hence, a possible mechanism may involve the cGMP-activated kinase, even though other mechanisms cannot be excluded.
authors.affiliation: Institute of Biology, University of Southern Denmark, Odense University, Campusvej 55, DK-5230 Odense M, Denmark.
authors.forename: Christian K
authors.initials: CK
authors.lastname: Tipsmark
authors.forename: Steffen S
authors.initials: SS
authors.lastname: Madsen
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D006152:Cyclic GMP / Q000494:pharmacology; D005880:Gills / Q000187:drug effects*; D066298:In Vitro Techniques; D007668:Kidney / Q000187:drug effects*; D009569:Nitric Oxide / Q000494:pharmacology*; D009599:Nitroprusside / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*; D014337:Trout / Q000378:metabolism*; D014882:Water-Electrolyte Balance / Q000187:drug effects
chemical_list: D009599:Nitroprusside; D009569:Nitric Oxide; D000254:Sodium-Potassium-Exchanging ATPase; D006152:Cyclic GMP