J. Terris et al., LONG-TERM REGULATION OF 4 RENAL AQUAPORINS IN RATS, American journal of physiology. Renal, fluid and electrolyte physiology, 40(2), 1996, pp. 414-422
The aquaporins are molecular water channels expressed in the kidney an
d other organs. To investigate long-term regulation of renal expressio
n of these water channels, we carried out immunoblotting studies using
membrane fractions from rat renal cortex and medulla. Both 48-h water
restriction in Sprague-Dawley rats and 5-day arginine vasopressin (AV
P) infusion in Brattleboro rats caused significant increases in the ex
pression levels of two aquaporins, aquaporin-2 and aquaporin-3, while
the levels of aquaporin-1 and aquaporin-4 were unchanged. The increase
s in aquaporin-2 and aquaporin-3 expression were seen in inner and out
er medulla as well as cortex. Ablation of the corticomedullary interst
itial osmotic gradient with an infusion of furosemide did not eliminat
e the upregulatory response to AVP infusion in Brattleboro rats. Furth
ermore, 5-day furosemide infusion to Sprague-Dawley rats did not decre
ase expression levels of the collecting duct aquaporins, but rather in
creased them. We conclude that the expression of aquaporin-2 and aquap
orin-3, but not aquaporin-1 or aquaporin-4, is increased in response t
o elevated circulating AVP. Because regulation of aquaporin-2 and aqua
porin-3 levels was observed in the cortex and because osmotic gradient
ablation did not abrogate the increase, we conclude that changes in i
nterstitial osmolality are not necessary for the AVP-induced upregulat
ion of aquaporin-2 and aquaporin-3 expression.