Flow regulation of endothelin-1 production in the inner medullary collecting duct

Abstract

Collecting duct-derived endothelin (ET)-1 is an autocrine inhibitor of Na(+) and water reabsorption; its deficiency causes hypertension and water retention. Extracellular fluid volume expansion increases collecting duct ET-1, thereby promoting natriuresis and diuresis; however, how this coupling between volume expansion and collecting duct ET-1 occurs is incompletely understood. One possibility is that volume expansion increases tubular fluid flow. To investigate this, cultured IMCD3 cells were subjected to static or flow conditions. Exposure to a shear stress of 2 dyn/cm(2) for 2 h increased ET-1 mRNA content by ∼2.3-fold. Absence of perfusate Ca(2+), chelation of intracellular Ca(2+), or inhibition of Ca(2+) signaling (calmodulin, Ca(2+)/calmodulin-dependent kinase, calcineurin, PKC, or phospholipase C) prevented the flow response. Evaluation of possible flow-activated Ca(2+) entry pathways revealed no role for transient receptor potential (TRP)C3, TRPC6, and TRPV4; however, cells with TRPP2 (polycystin-2) knockdown had no ET-1 flow response. Flow increased intracellular Ca(2+) was blunted in TRPP2 knockdown cells. Nonspecific blockade of P2 receptors, as well as specific inhibition of P2X7 and P2Y2 receptors, prevented the ET-1 flow response. The ET-1 flow response was not affected by inhibition of either epithelial Na(+) channels or the mitochondrial Na(+)/Ca(2+) exchanger. Taken together, these findings provide evidence that in IMCD3 cells, flow, via polycystin-2 and P2 receptors, engages Ca(2+)-dependent signaling pathways that stimulate ET-1 synthesis.

Activation of purinergic receptors (P2) in the renal medulla promotes endothelin-dependent natriuresis in male rats

“…This is in line with recent findings demonstrating that blockade of P2Y 2 and P2X 7 receptors inhibits ET-1 production in inner medullary collecting duct cells (22). Furthermore, nonrenal studies demonstrated that purinergic and ET-1 signaling interact in sensory neurons (5), blood vessels (1, 13), as well as myocardium (10).…”

“…Our findings suggest that the purinergic receptors might be involved. This idea is originally based on a recent study revealing that P2 receptors are required for flow-stimulated ET-1 release in inner medullary collecting duct cells (22). Our data showed that blockade of medullary P2 receptors by suramin inhibited the diuretic and natriuretic response to increased medullary NaCl loading.…”

“…Several earlier studies suggest that extracellular osmolality enhances ET-1 production and release by freshly isolated or cultured renal tubular or collecting duct cells (9,16,22,33). This in vitro evidence was supported by in vivo studies from our lab showing that infusion of hyperosmotic saline into the renal medulla resulted in diuresis, natriuresis, and increases in urinary ET-1 excretion (6).…”

“…Thus, there is fairly clear evidence to suggest that ET-1 and purinergic receptors are important in controlling renal tubular reabsorption of Na ϩ and water. The tubular segment contributing to the interaction between ET-1 and purinergic receptors in controlling Na ϩ excretion is not specifically known; however, the inner medullary collecting ducts are potential contributors based on recent data (22). Roles for proximal tubule and thick ascending limb are also postulated.…”

“…However, the interaction between renal ET-1 and purinergic signaling is relatively unexplored. Recently, it has been demonstrated that renal P2Y 2 and P2X 7 receptor blockade inhibits ET-1 production in inner medullary collecting duct cells (22). However, the interaction between the endothelin and the purinergic signaling systems within the renal medulla has yet to be explored in vivo.…”