Cloning and functional characterization of a novel aquaporin from Xenopus laevis oocytes.
We have cloned a novel aquaporin (AQP) from Xenopus laevis oocytes, which we have provisionally named AQPxlo. The predicted protein showed highest homology (39-50%) to aquaglyceroporins. Northern blot analysis showed strong hybridization to an approximately 1.4-kb transcript in X. laevis fat body and oocytes, whereas a weaker signal was obtained in kidney. We injected in vitro transcribed cRNA encoding AQPxlo into Xenopus oocytes for functional characterization. AQPxlo expression increased osmotic water permeability (P(f)), as well as the uptake of glycerol and urea. However, AQPxlo excluded larger polyols and thiourea. An alkaline extracellular pH (pH(o)) increased P(f) and to a lesser extent urea uptake but not glycerol uptake. Remarkably, low HgCl(2) concentrations (0.3-10 microm) reduced P(f) and urea uptake, whereas high concentrations (300-1000 microm) reversed the inhibition. We propose that AQPxlo is a new AQP paralogue unknown in mammals.
Virkki
Leila V
LV
Department of Cellular and Molecular Physiology, Yale University School of Medicine, PO Box 108026, 333 Cedar Street, New Haven, CT 06520, USA. leila.virkki@yale.edu
Franke
Christina
C
Somieski
Petra
P
Boron
Walter F
WF
D000595:Amino Acid Sequence; D000818:Animals; D020346:Aquaporins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D003001:Cloning, Molecular; D017931:DNA Primers; D018076:DNA, Complementary; D005990:Glycerol / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D009865:Oocytes / Q000378:metabolism*; D051381:Rats; D017386:Sequence Homology, Amino Acid; D014508:Urea / Q000378:metabolism; D014982:Xenopus laevis
D020346:Aquaporins; D017931:DNA Primers; D018076:DNA, Complementary; D014508:Urea; D005990:Glycerol