Abstract 534: Cytochrome P450 epoxygenase regulates Na transport in aldosterone-sensitive distal nephron: a lesson learns from Cyp2c44 knockout mice

Abstract

Previous study demonstrated that the down-regulation of epoxygenase caused salt-sensitive hypertension. We used the real-time PCR technique to demonstrate that a high Na (4% Na) intake increased the Cyp2c44 expression in the thick ascending limb and distal convoluted tubule (DCT) and connecting tubule (CNT). The disruption of cyp2c44 increased ENaC activity in CNT and the 40 pS inwardly-rectifying K channel, a heterotetramer of Kir.4.1/Kir5.1, in the basolateral membrane of early segment of DCT (DCT1). Application of epoxyeicosatrienoic acid (EET) inhibited both ENaC in the CNT and the Kir4.1/5.1 channels in DCT1. Kir4.1/5.1 plays a key role in generating the cell membrane potential in the DCT and is the only type of K channels responsible for providing K conductance in the basolateral membrane of the DCT. Also, we demonstrated that Kir.4.1/5.1 activity determines the apical NCC expression and Ste20-related-proline-alanine-rich kinase (SPAK) which stimulates NCC activity through the phosphorylation of NCC. Since EET inhibited Kir4/1/5.1 in the DCT, the disruption of Cyp2c44 significantly increased the basolateral Kir4.1/5.1 activity thereby increasing the expression of SPAK and NCC in cyp2c44 knockout mice. Thus, feeding Kcnj10 knockout mice with high Na caused hypertension. Moreover, the application of amiloride failed to completely reverse the Na-sensitive hypertension in the knockout mice while the application of thiazide and amiloride restored the normal blood pressure in Kcnj10 knockout mice. We conclude that Cyp2c44 plays an important role in suppressing NCC in the DCT and ENaC in the CNT during increasing dietary Na intake. The upregulation of NCC expression in Kcnj10 -/- mice was due to the stimulation of the basolateral K channels in the DCT.