Effects of 20-HETE on Na⁺ transport and Na⁺-K ⁺-ATPase activity in the thick ascending loop of Henle

Previous studies have indicated that 20-hydroxyeicosatetraenoic acid (20-HETE) inhibits Na⁺ transport in the medullary thick ascending loop of Henle (mTALH), but the mechanisms involved remain uncertain. The present study compared the effects of 20-HETE with those of ouabain and furosemide on intracellular Na⁺ concentration ([Na⁺]_i), Na⁺-K⁺-ATPase activity, and ⁸⁶Rb⁺ uptake, an index of Na⁺ transport, in mTALH isolated from rats. Ouabain (2 mM) increased, whereas furosemide (100 μM) decreased, [Na ⁺]_i in the mTALH of rats. Ouabain and furosemide inhibited ⁸⁶Rb⁺ uptake by 91 and 30%, respectively. 20-HETE (1 μM) had a similar effect as ouabain and increased [Na⁺] _i from 19 ± 1 to 30 ± 1 mM. 20-HETE reduced Na ⁺-K⁺-ATPase activity by 30% and ⁸⁶Rb ⁺ uptake by 37%, but it had no effect on ⁸⁶Rb⁺ uptake or [Na⁺]_i in the mTALH of rats pretreated with ouabain. 20-HETE inhibited ⁸⁶Rb⁺ uptake by 12% and increased [Na⁺]_i by 19 mM in mTALH pretreated with furosemide. These findings indicate that 20-HETE secondarily inhibits Na ⁺ transport in the mTALH of the rat, at least, in part by inhibiting the Na⁺-K⁺-ATPase activity and raising [Na ⁺]_i.