Na delivery, ENaC and mitochondrial NCX mediate flow‐stimulated collecting duct ET‐1 production

Abstract

Collecting duct (CD) endothelin‐1 (ET‐1) inhibits Nareabsorption; its deficiency causes marked hypertension. CD ET‐1 is increased by volume expansion and fluid flow, suggesting coupling of CD Nadelivery to ET‐1 synthesis. To assess this, we studied the effect of Naon flow‐regulated ET‐1 production by mpkCCDc14 cells. Cells were subjected to static conditions or 2 dyne/cm2 for 2 hr, followed by determination of ET‐1 mRNA (N=7–12 all conditions). Flow with 300 mOsm/L NaCl increased ET‐1 mRNA levels to 165% of that seen under static conditions. Increasing media osmolarity to 450 mOsm/L with NaCl or sodium acetate, but not mannitol or choline Cl further augmented the ET‐1 flow response. Decreasing Na to 150 mOsm/L while adjusting to 300 mOsm/L with urea, mannitol or choline chloride reduced the flow response. Inhibition of ENaC with amiloride or benzamil prevented the ET‐1 flow response. Aldosterone almost doubled the flow response. Given that we have previously shown that calcium controls CD ET‐1 production, the effect of Na/Ca exchanger (NCX) blockade was assessed. SEA0400, a plasma membrane NCX inhibitor, did not affect the ET‐1 flow response. However, CGP37157, a mitochondrial NCX inhibitor, almost abolished the flow response. These data suggest that flow‐stimulated CD ET‐1 mRNA is mediated by Na entry via ENaC, resulting in mitochrondrial NCX‐induced increased [Ca]i and ultimately ET‐1 gene transcription.