cAMP-dependent fluid secretion in rat inner medullary collecting ducts

• Published in: American journal of physiology. Renal physiology 2001-06, Vol.280 (6), p.F1019-F1029
• Main Authors: Wallace, D P, Rome, L A, Sullivan, L P, Grantham, J J
• Format: Article
• Language: English
• Subjects: 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid - pharmacology; 8-Bromo Cyclic Adenosine Monophosphate - pharmacology; Amiloride - analogs & derivatives; Amiloride - pharmacology; Animals; Barium - pharmacology; Biological Transport - drug effects; Biological Transport - physiology; Blood Proteins - pharmacology; Calcium Channel Blockers - pharmacology; Chlorides - metabolism; Cyclic AMP - metabolism; Cyclic AMP-Dependent Protein Kinases - antagonists & inhibitors; Cystic Fibrosis Transmembrane Conductance Regulator - metabolism; Dissection; Enzyme Inhibitors - pharmacology; Glyburide - pharmacology; Hypoglycemic Agents - pharmacology; Isoquinolines - pharmacology; Kidney Medulla - metabolism; Kidney Tubules, Collecting - metabolism; Male; ortho-Aminobenzoates - pharmacology; Ouabain - pharmacology; Rats; Rats, Sprague-Dawley; Sodium Chloride - pharmacokinetics; Sulfonamides; Vanadates - pharmacology; Water - metabolism; Water-Electrolyte Balance - physiology
• ISSN: 1931-857X; 1522-1466
• DOI: 10.1152/ajprenal.2001.280.6.f1019

We used an unambiguous in vitro method to determine if inner medullary collecting ducts (IMCD) have intrinsic capacities to absorb and secrete solutes and fluid in an isotonic medium. IMCD(1), IMCD(2), and IMCD(3) were dissected from kidneys of young Sprague-Dawley rats. 8-Bromo-3',5'-cyclic monophosphate (8-BrcAMP) stimulated lumen formation and progressive dilation in all IMCD subsegments; lumen formation was greatest in IMCD(1.) Benzamil potentiated the rate of lumen expansion in response to 8-BrcAMP. Fluid entered tubule lumens by transcellular secretion rather than simple translocation of intracellular fluid. Secreted lumen solutes were osmometrically active. Inhibition of protein kinase A with H-89 and Rp diastereomer of adenosine 3',5'-cyclic monophosphorothioate blocked fluid secretion. The rate of lumen expansion was reduced by the selective addition of ouabain, barium, diphenyl-2-carboxylate, bumetanide, glybenclamide, or DIDS, or reduction of extracellular Cl(-). We conclude that IMCD absorb and secrete electrolytes and fluid in vitro and that secretion is accelerated by cAMP. We suggest that salt and fluid secretion by the terminal portions of the renal collecting system may have a role in modulating the composition and volume of the final urine.