Interaction between NO synthase and NADPH oxidase in control of sodium transport by the renal thick ascending limb during diabetes

Aim During type 1 diabetes ( T 1 D ), the medullary thick ascending limb (m TAL ) displays an NADPH oxidase‐dependent increase in sodium transport, in concert with increased NO production by NO synthase 1 ( NOS 1) and NOS 2. We hypothesized that NOS 1‐ and/or NOS 2‐derived NO blunts T 1 D ‐induced activation of sodium transport in the m TAL . Methods T1D was induced by streptozotocin injection ( STZ rats); sham rats received vehicle. Three‐to‐four weeks later, m TAL were isolated from both groups for assay of nitrite and superoxide production, and O 2 consumption in the absence or presence of various inhibitors. Results Apocynin ( NADPH oxidase inhibitor) normalized superoxide production and ouabain‐sensitive O 2 consumption and furosemide‐sensitive O 2 consumption by m TAL s from STZ rats, without altering O 2 consumption by m TAL s from sham rats. Apocynin also unmasked a T 1D‐induced increase in nitrite production. NOS inhibition did not alter superoxide production in either group. In sham mTAL , total NOS inhibition, but not isoform‐specific inhibition of NOS 1 or NOS 2, increased ouabain‐ and furosemide‐sensitive O 2 consumption, confirming a tonic inhibitory impact of NOS 3 on sodium transport. In contrast, neither total nor isoform‐specific NOS inhibition altered O 2 consumption by STZ mTAL . Apocynin treatment of STZ m TAL unveiled the ability of isoform‐specific NOS inhibition to significantly increase O 2 consumption, without further increase in O 2 consumption with total NOS inhibition. Conclusion Under normal conditions, NOS 3‐derived NO inhibits sodium transport in the mTAL . T 1 D dismantles the impact of NOS ‐mediated inhibition of sodium transport as a result of NADPH oxidase‐dependent NO scavenging. Inhibition of NADPH oxidase to preserve NO bioavailability reveals an inhibitory impact of NOS 1‐ and NOS 2‐derived NO on sodium transport in the m TAL .