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WATER AND ELECTROLYTE HOMEOSTASIS

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

Departments of ¹Physiology and ²Medicine and ³Kidney Disease Center, Medical College of Wisconsin, Milwaukee, Wisconsin; ⁴Department of Biochemistry and Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas

Submitted 10 November 2006 ; accepted in final form 9 February 2007

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.

cytochrome P-4504A; 20-hydroxyeicosatetraenoic acid; sodium-potassium-adenosinetriphosphatase; medullary thick ascending loop of Henle; kidney; rat