title: Aquaporin 2 expression increased by glucagon in normal rat inner medullary collecting ducts.
abstract: It is well known that Glucagon (Gl) is released after a high protein diet and participates in water excretion by the kidney, principally after a protein meal. To study this effect in in vitro perfused inner medullary collecting ducts (IMCD), the osmotic water permeability (Pf; mum/s) at 37 degrees C and pH 7.4 in normal rat IMCDs (n = 36) perfused with Ringer/HCO(3) was determined. Gl (10(-7) M) in absence of Vasopressin (AVP) enhanced the Pf from 4.38 +/- 1.40 to 11.16 +/- 1.44 microm/s (P < 0.01). Adding 10(-8), 10(-7), and 10(-6) M Gl, the Pf responded in a dose-dependent manner. The protein kinase A inhibitor H8 blocked the Gl effect. The specific Gl inhibitor, des-His(1)-[Glu(9)] glucagon (10(-7) M), blocked the Gl-stimulated Pf but not the AVP-stimulated Pf. There occurred a partial additional effect between Gl and AVP. The cAMP level was enhanced from the control 1.24 +/- 0.39 to 59.70 +/- 15.18 fm/mg prot after Gl 10(-7) M in an IMCD cell suspension. The immunoblotting studies indicated an increase in AQP2 protein abundance of 27% (cont 100.0 +/- 3.9 vs. Gl 127.53; P = 0.0035) in membrane fractions extracted from IMCD tubule suspension, incubated with 10(-6) M Gl. Our data showed that 1) Gl increased water absorption in a dose-dependent manner; 2) the anti-Gl blocked the action of Gl but not the action of AVP; 3) Gl stimulated the cAMP generation; 4) Gl increased the AQP2 water channel protein expression, leading us to conclude that Gl controls water absorption by utilizing a Gl receptor, rather than a AVP receptor, increasing the AQP2 protein expression.
authors.affiliation: Laboratório de Pesquisa Básica-LIM 12, Hospital das Clínicas da Faculdade de Medicina-Nefrologia, Universidade de São Paulo, Av Dr Arnaldo, 455 São Paulo-SP 01246-903, Brazil.
authors.forename: Yuristella
authors.initials: Y
authors.lastname: Yano
authors.forename: Katia R
authors.initials: KR
authors.lastname: Cesar
authors.forename: Magali
authors.initials: M
authors.lastname: Araujo
authors.forename: Adilson C
authors.initials: AC
authors.lastname: Rodrigues
authors.forename: Lucia C
authors.initials: LC
authors.lastname: Andrade
authors.forename: Antonio J
authors.initials: AJ
authors.lastname: Magaldi
mesh_terms: D000818:Animals; D051399:Aquaporin 2 / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005934:Glucagon / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D007546:Isoquinolines / Q000494:pharmacology; D007679:Kidney Medulla / Q000166:cytology / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000378:metabolism*; D008297:Male; D009995:Osmosis; D051381:Rats; D017208:Rats, Wistar; D014667:Vasopressins / Q000494:pharmacology
chemical_list: C496025:Aqp2 protein, rat; D051399:Aquaporin 2; D007546:Isoquinolines; D014667:Vasopressins; C053177:N-(2-(methylamino)ethyl)-5-isoquinolinesulfonamide; D005934:Glucagon; D000242:Cyclic AMP