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Division of Nephrology, University of Utah Health Sciences Center, Salt Lake City, Utah 84132; and Salt Lake Veterans Affairs Medical Center, Salt Lake City, Utah 84148
To whom requests for reprints should be addressed at 1 Division of Nephrology, University of Utah Health Sciences Center, 1900 East, 30 North, Salt Lake City, UT 84132. E-mail: donald.kohan{at}hsc.utah.edu
Abstract
Adenosine triphosphate (ATP) and endothelin (ET)-1 inhibit vasopressin-stimulated water reabsorption in the inner medullary collecting duct (IMCD). Because both ATP and ET-1 are released by the IMCD and can act in an autocrine manner to regulate IMCD water transport, we sought to determine whether these factors can modulate the other’s production. To begin such studies, the effect of ATP on IMCD ET-1 production was examined. ATP caused a dose-dependent inhibition of ET-1 release and inhibited ET-1 mRNA levels in primary cultures of rat IMCD cells. This effect was first evident after 4 hrs of exposure to ATP and persisted for at least 24 hrs. The 50% inhibitory concentration for ATP inhibition of ET-1 production was approximately 1 µM, and the maximal response was observed at 25–100 µM. ATP acted, at least in part, through the P2Y2 receptor because its effect was mimicked by UTP, but not by the P2X agonist, 
,ß-methylene–ATP. N-methyl-L-arginine, or indomethacin, did not block the ATP inhibitory effect. In summary, these data demonstrate that ATP inhibits IMCD ET-1 protein and mRNA accumulation, that this is mediated via P2Y receptors, and that the ATP effect is independent of cyclooxygenase or nitric oxide synthase metabolites. These findings suggest that although ATP and ET-1 both antagonize vasopressin action in the IMCD, they may have a complex interaction that ultimately determines the degree to which they each participate in modulating collecting duct function.
Key Words: endothelin-1 • purinergic • P2Y • ATP • collecting duct
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