Aquaporin 2 expression increased by glucagon in normal rat inner medullary collecting ducts

Am J Physiol Renal Physiol. 2009 Jan;296(1):F54-9. doi: 10.1152/ajprenal.90367.2008. Epub 2008 Oct 1.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Aquaporin 2 / metabolism*
  • Cyclic AMP / metabolism
  • Dose-Response Relationship, Drug
  • Glucagon / antagonists & inhibitors
  • Glucagon / metabolism
  • Glucagon / physiology*
  • Isoquinolines / pharmacology
  • Kidney Medulla / cytology
  • Kidney Medulla / metabolism*
  • Kidney Tubules, Collecting / cytology
  • Kidney Tubules, Collecting / metabolism*
  • Male
  • Osmosis
  • Rats
  • Rats, Wistar
  • Vasopressins / pharmacology

Substances

  • Aqp2 protein, rat
  • Aquaporin 2
  • Isoquinolines
  • Vasopressins
  • N-(2-(methylamino)ethyl)-5-isoquinolinesulfonamide
  • Glucagon
  • Cyclic AMP