Role of 20-HETE in D1/D2 dopamine receptor synergism resulting in the inhibition of Na+-K+-ATPase activity in the proximal tubule

Abstract

Previous studies propose 20-hydroxyeicosatetraenoic acid (20-HETE), a major arachidonic acid metabolite of cytochrome P-450 (CYP), as a possible mediator of Na+-K+-ATPase inhibition by dopamine (DA). The aim of this study was to investigate the intracellular mechanisms involved in this effect and to elucidate the DA receptor associated with the 20-HETE pathway in the rat kidney. DA (10−5M) inhibited Na+-K+-ATPase activity in microdissected tubular segments to 59.4 ± 3.8% of control activity. This response was suppressed by the CYP4A inhibitor 17-octadecynoic acid (10−6M), which had no effect per se, thus confirming the participation of CYP arachidonic acid metabolites in DA-induced Na+-K+-ATPase inhibition. We next examined whether 20-HETE is involved in the signaling pathways triggered by either D1or D2receptors. Neither fenoldopam nor quinpirole (D1and D2agonists, respectively, both 10−5M) modified Na+-K+-ATPase activity when tried alone. However, coincubation of a threshold concentration of 20-HETE (10−9M) with fenoldopam resulted in a synergistic inhibition of Na+-K+-ATPase activity (66 ± 2% of control activity), while 20-HETE plus quinpirole had no effect. Furthermore, 20-HETE (10−9M) synergized with forskolin (10−5M) and with the diacylglycerol analog 1-oleoyl-2-acetoyl- sn-glycerol (OAG; 10−11M; 62.0 ± 5.3 and 69.9 ± 2.0% of control activity, respectively), indicating a cooperative role of 20-HETE with the D1-triggered pathways. In line with these results, no additive effect was observed when OAG and 20-HETE were combined at concentrations which per se produced maximal inhibition (10−6M). These results demonstrate that the inhibition of Na+-K+-ATPase activity by DA in the proximal tubule may be the result of the synergism between 20-HETE and the D1signaling pathway.