title: Differential effects of hyperosmolality on Na-K-ATPase and vasopressin-dependent cAMP generation in the medullary thick ascending limb and outer medullary collecting duct.
abstract: Hyperosmolality in the renal medullary interstitium is generated by the renal countercurrent multiplication system, in which the medullary thick ascending limb (MAL) and the outer medullary collecting duct (OMCD) primarily participate. Since arginine vasopressin (AVP) regulates Na-K-ATPase activity directly via protein kinase A and indirectly via hyperosmolality, we investigated the acute and chronic effects of hyperosmolality on Na-K-ATPase and AVP-dependent cAMP generation in the MAL and OMCD. Microdissected MAL and OMCD from control and dehydrated rats were used for the measurement of Na-K-ATPase activity, mRNA expression of alpha-1, beta-1, and beta-2 subunits of Na-K-ATPase, and AVP-dependent cAMP generation. Na-K-ATPase activity in the MAL from dehydrated rats, as measured in isotonic medium, was higher than that of control rats. Moreover, incubation of samples in hypertonic medium (490 mOsm/kg H2O) further increased Na-K-ATPase activity. Dehydration increased alpha-1, beta-1, and beta-2 mRNA expression in the MAL without changing that in the OMCD. Western blot analysis revealed that in the outer medulla, the expression of beta-1, but not that of alpha-1 or beta-2, was stimulated by dehydration. Incubation of MAL or OMCD in hypertonic medium increased AVP-dependent cAMP generation. Higher levels of AVP-dependent cAMP were generated in the MAL from dehydrated rats than that of controls, although incubation in hypertonic medium did not lead to additional increases in AVP-dependent cAMP accumulation. In contrast, AVP-dependent cAMP generation in the OMCD was stimulated by dehydration, and was further stimulated by incubation in hypertonic medium. These findings demonstrate that Na-K-ATPase is upregulated short- and long-term hyperosmolality in the MAL, but not in OMCD.
authors.affiliation: Department of Nephrology, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Yoriko
authors.initials: Y
authors.lastname: Sakuma
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nonoguchi
authors.forename: Masanobu
authors.initials: M
authors.lastname: Takayama
authors.forename: Tianxin
authors.initials: T
authors.lastname: Yang
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Terada
authors.forename: Takeaki
authors.initials: T
authors.lastname: Inoue
authors.forename: Yushi
authors.initials: Y
authors.lastname: Nakayama
authors.forename: Yukimasa
authors.initials: Y
authors.lastname: Kohda
authors.forename: Sei
authors.initials: S
authors.lastname: Sasaki
authors.forename: Kimio
authors.initials: K
authors.lastname: Tomita
mesh_terms: D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology / Q000502:physiology*; D015153:Blotting, Western; D000242:Cyclic AMP / Q000378:metabolism*; D003681:Dehydration / Q000503:physiopathology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006982:Hypertonic Solutions; D007552:Isotonic Solutions; D007679:Kidney Medulla / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D008138:Loop of Henle / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D009281:Naphthalenes / Q000494:pharmacology; D009994:Osmolar Concentration; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D006982:Hypertonic Solutions; D007552:Isotonic Solutions; D009281:Naphthalenes; D012333:RNA, Messenger; D001127:Arginine Vasopressin; D000242:Cyclic AMP; D000254:Sodium-Potassium-Exchanging ATPase; C058819:calphostin C