20-HETE mediates the effect of parathyroid hormone and protein kinase C on renal phosphate transport

Abstract

Parathyroid hormone (PTH) is a major inhibitor of renal proximal tubule (PT) sodium-dependent phosphate (Na +Pi) cotransport. PTH is thought to exert its effect on Pi transport in the PT via the protein kinase A (PKA) and C (PKC) intracellular signalling pathways. PKC-dependent phosphorylation of phospholipase A 2 stimulates arachidonic acid (AA) release, the latter a potent inhibitor of Pi transport. In turn, AA is metabolized to 20-hydroxyeicosatetraenoic acid (20-HETE) in the PT. In addition, 20-HETE production is stimulated by PTH. We therefore explored the possibility that 20-HETE may mediate the PTH/PKC inhibition of renal Na +Pi cotransport. To this end, we tested the effect of 20-HETE on Na +Pi cotransport in proximal tubule-like cells. Exposure of opossum kidney (OK) cells for 4 h to 20-HETE (10 −7 M) decreased Na +-dependent uptake of 32Pi (from 0.26 ± 0.02 to 0.19 ± 0.01 nmol/mg protein.min) by ∼25% ( P < 0.001). The inhibition was due to a reduction in V max. 20-HETE had no significant effect on either the apical amiloride-sensitive and insensitive 22Na uptakes or on basolateral ouabainsensitive 86Rb uptake, and was specific for Pi. These results indicate that 20-HETE specifically inhibits Na +-dependent Pi transport in OK cells and that it may be a mediator of PTH action in the PT.