Fig. 3. The effect of the nitric oxide (NO) donors sodium nitroprusside (SNP; 1 mmol l^–1) and papa-nonoate (NOC-15; 0.2 mmol l^–1) on in situ Na⁺/K⁺-ATPase activity (measured as ouabain-sensitive Rb⁺ uptake) in kidney (A) and gill (B) tissue. Samples were pre-incubated for 10 min with the NO donors before the Rb⁺ uptake assay. Different letters indicate significant difference (P<0.05). Values are means ± S.E.M. (N=8).