Flow stimulates inner medullary collecting duct endothelin‐1 production

Abstract

Collecting duct (CD)‐derived endothelin‐1 (ET‐1) inhibits Na and water reabsorption; its deficiency causes marked hypertension. CD ET‐1 synthesis is enhanced by extracellular fluid volume expansion. In cultured cortical CD (CCD) cells, increased flow (as would occur in tubule fluid during volume expansion) stimulates ET‐1 production; this is ENaC‐dependent. Since the inner medullary CD (IMCD) is the major site of renal ET‐1 synthesis, we examined the effect of flow on IMCD ET‐1 production. Mouse IMCD3 cells were subjected to static conditions or flow (2 dyne/cm2 for 2 hr), followed by determination of ET‐1 mRNA. Flow increased ET‐1 mRNA by 2.2‐fold. Absence of perfusate Ca prevented the flow response. BAPTA, W‐7, calmidazolium, KN‐93, calphostin C and cyclosporin A reduced the ET‐1 flow response, indicating that PKC and Ca/calmodulin/calmodulin kinase/calcineurin pathways are essential for the flow response. Amiloride or benzamil did not affect the ET‐1 response to flow. Increasing perfusate osmolality to 450 mOsm with NaCl, mannitol or urea elicited a marked flow response (4.4‐fold increase in ET‐1 mRNA). Removal of cilia with chloral hydrate reduced the flow response, while flow failed to stimulate ET‐1 mRNA in mIMCD3 cells deficient in polycystin‐2. These data suggest that IMCD ET‐1 synthesis is stimulated by tubule fluid flow via increased solute delivery and possibly cilia deformation which in turn activates PKC‐ and Ca‐dependent pathways. We propose that Na delivery stimulates CCD ET‐1 which, in turn, inhibits CCD Na reabsorption, while solute and water delivery stimulate IMCD ET‐1 which, in turn, inhibits IMCD water and urea reabsorption.