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Adrenergic regulation of salt and fluid secretion in human medullary collecting duct cells

¹Kidney Institute and Departments of ²Internal Medicine and ³Urology, University of Kansas Medical Center, Kansas City, Kansas 66160

Submitted 22 December 2003 ; accepted in final form 22 June 2004

Transepithelial salt and fluid secretion mediated by cAMP in initial inner medullary collecting ducts (IMCD_i) may be important for making final adjustments to urine composition. We examined in primary cultures of human IMCD_i cells the effects of adrenergic receptor (AR) agonists and antagonists on intracellular cAMP levels, short-circuit current (I_SC), and fluid secretion. Epinephrine (1 µM), norepinephrine (1 µM), and isoproterenol (10 nM) individually increased intracellular cAMP levels 57-, 2-, and 25-fold, respectively, and stimulated I_SC 3.3-, 2.9-, and 3.4-fold, respectively. -AR activation increased net fluid secretion by cultured human IMCD_i cell monolayers from 0.09 ± 0.04 to 0.26 ± 0.05 µl·h^–1·cm^–2 and freshly isolated rat IMCD_i from 0.02 ± 0.01 to 0.09 ± 0.02 nl·h^–1·mm^–1. In monolayers, these effects were eliminated by blocking ₂-AR, but not ₁-AR. Activation of ₂-AR with guanabenz inhibited isoproterenol-induced I_SC by 37% in human IMCD_i monolayers and fluid secretion by 91% in rat IMCD_i. Immunohistochemistry of human medullary tissue sections revealed greater expression of ₂-AR than ₁-AR; ₂-AR was localized to the basolateral membranes of human IMCD_i. Immunoblots identified _2A-AR and _2B-AR in cultured human IMCD_i cell monolayers. We conclude that 1) catecholamines stimulate cAMP-dependent anion and fluid secretion by IMCD_i cells primarily through ₂-AR activation and 2) ₂-AR activation attenuates cAMP-dependent anion secretion.

chloride transport; catecholamines; epinephrine; cystic fibrosis transmembrane conductance regulator; NKCC1

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