Permeabilities to glycerol an
d small non-electrolytes of three Aquaporin 1 CHIP (AQP1) water channels were measure
d in AQP1 cRNA-injecte
d Xenopus laevis oocytes an
d in human AQP1 channels reconstitute
d in proteoliposomes. By an dquo" align="MIDDLE" BORDER="0">osmoticdquo" align="MIDDLE" BORDER="0"> swelling assay, significant increases of ethylene glycol, glycerol an
d 1,3-propane
diol apparent permeability coefficients (
Psolutes) were foun
d in oocytes expressing human, rat an
d frog AQP1.
p-Chloromercuribenzene sulphonate (
PCMBS) an
d CuSO
4 inhibite
d, by 95% an
d 58% respectively, apparent glycerol permeability (
P
gly) in oocytes expressing human AQP1.
pCMBS inhibition was reverse
d by -mercaptoethanol an
d CuSO
4 inhibition was partly reverse
d by the Cu
2+-bin
ding pepti
de Gly-Gly-His. Tritiate
d glycerol uptakes confirme
d the augmente
d P
gly value of AQP1 cRNA-injecte
d oocytes. In contrast, no increases of urea,
meso-erythritol, D- or L-threitol, xylitol an
d mannitol uptakes were
detecte
d. Stoppe
d-flow light scattering experiments performe
d with human AQP1 proteoliposomes also reveale
d a much greater increase of
P
gly than
di
d those with protein-free liposomes; the initial rate of proteoliposomes also swelling was inhibite
d by 96.2% with HgCl
2 an
d by 72.5% with CuSO
4. In AQP1 cRNA-injecte
d oocytes an
d in proteoliposomes, the value of the glycerol reflection coefficient was 0.74–0.80, in
dicating that water an
d glycerol share the same pathway. All these results provi
de strong evi
dence that water an
d certain small solutes permeate the AQP1 channels expresse
d at the surface of
X. laevis oocytes or reconstitute
d in proteoliposomes. The urea exclusion suggests that the selectivity of the AQP1 channels not only
depen
ds on the size of the solutes but probably also on their flexibility an
d their ability to form H-bon
ds.
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