NADPH Oxidase and PKC Contribute to Increased Na Transport by the Thick Ascending Limb During Type 1 Diabetes

Abstract

—Type 1 diabetes triggers protein kinase C (PKC)-dependent NADPH oxidase activation in the renal medullary thick ascending limb (mTAL), resulting in accelerated superoxide production. As acute exposure to superoxide stimulates NaCl transport by the mTAL, we hypothesized that diabetes increases mTAL Na + transport through PKC-dependent and NADPH oxidase–dependent mechanisms. An O 2 -sensitive fluoroprobe was used to measure O 2 consumption by mTALs from rats with streptozotocin-induced diabetes and sham rats. In sham mTALs, total O 2 consumption was evident as a 0.34±0.03 U change in normalized relative fluorescence (ΔNRF)/min per mg protein. Ouabain (2 mmol/L) reduced O 2 consumption by 69±4% and 500 μmol/L furosemide reduced O 2 consumption by 58±8%. Total O 2 consumption was accelerated in mTAL from diabetic rats (0.74±0.07 ΔNRF/min/mg protein; P <0.05 versus sham), reflecting increases in ouabain- and furosemide-sensitive O 2 consumption. NADPH oxidase inhibition (100 μmol/L apocynin) reduced furosemide-sensitive O 2 consumption by mTAL from diabetic rats to values not different from sham. The PKC inhibitor calphostin C (1 μmol/L) or the PKCα/β inhibitor Gö6976 (1 μmol/L) decreased furosemide-sensitive O 2 consumption in both groups, achieving values that did not differ between sham and diabetic. PKCβ inhibition had no effect in either group. Similar inhibitory patterns were evident with regard to ouabain-sensitive O 2 consumption. We conclude that NADPH oxidase and PKC (primarily PKCα) contribute to an increase in O 2 consumption by the mTAL during type 1 diabetes through effects on the ouabain-sensitive Na + -K + -ATPase and furosemide-sensitive Na + -K + -2Cl − cotransporter that are primarily responsible for active transport Na + reabsorption by this nephron segment.