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Landmarks in the discovery of water channel proteins (aquaporins)
| 1896 |
Overton proposed the existence of aqueous patches in the plasma
membrane to explain permeability to water and small hydrophilic solutes
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| 1956 |
Stein and Danielli suggested that hydrophilic pores in the membrane
could account for the movement of water and ions
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1968–1983
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Solomon and coworkers estimated the equivalent radius of these
pores in the RBC membrane, concluding that it is large enough to permit
the passage of water, ions and non-electrolytes
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| 1970 |
Macey and Farmer observed that osmotic water permeability of human
RBCs could be inhibited by mercurials (PCMB and PCMBS) and this was
explained by closure of specific water channels (pores that are inaccessible
to both cations and anions)
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| 1975–1983 |
Sha’afi and coworkers and Solomon and coworkers performed
labeling experiments with sulfhydryl-reactive reagents without correlating
binding with inhibition of water transport; Solomon and coworkers
claimed that a protein migrating as band 3 on the electrophoretogram
of RBC membranes is a common pore for water, cations, anions and non-electrolytes
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| 1977–1985 |
Benga and coworkers extensively characterized the conditions of
inhibition of water channels in RBC and resealed ghosts by NMR, biochemical
methods and electron microscopy, and found a number of new features,
e.g. the water channels appeared impervious to proteolytic digestion
in intact cells
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| 1986 |
Benga and coworkers clearly demonstrated for the first time the
presence and location of a water channel in the human RBC membrane
among polypeptides migrating in the region of 35–60 kDa on the
electrophoretogram of RBC membranes, labeled with 203 Hg-PCMBS under
conditions for the specific inhibition of water diffusion; it was
also suggested that a minor membrane protein that binds PCMBS is involved
in water transport, and the way in which the specific protein could
be further characterized was indicated: by purification and reconstitution
in liposomes
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| 1988 |
Agre and coworkers identified a novel integral membrane protein
in human RBCs with a non-glycosylated component of 28 kDa and a glycosylated
component migrating as a diffuse band of 35–60 kDa; they suggested
that the new protein (called CHIP28 in 1991) may play a role in linkage
of the membrane skeleton to the lipid bilayer
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| 1990 |
Parker first suggested in personal discussion to Agre that the
novel protein may be the water channel
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| 1992 |
Agre and coworkers, following the suggestion of Windhager to use
oocyte expression as a mechanism to study water transporters, found
that oocytes from Xenopus Laevis microinjected with in vitro-transcribed
CHIP28 RNA exhibited increased osmotic water permeability. This was
inhibited by mercuric chloride, therefore, it was suggested that CHIP28
is a functional unit of membrane water channels; by reconstitution
in liposomes it was demonstrated that CHIP28 is a water channel itself
rather than a water channel regulator
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| 1993 |
CHIP28 was renamed aquaporin 1 (AQP1)
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| 1993–2002 |
More than 200 members of the aquaporin family have been found in
bacteria, plants, animals and humans; the physiological and pathological
implications are being uncovered |
From G.
Benga, Birth of water channel proteins––the aquaporins,
Cell Biology International, 27 (9), 2003, pp. 701-709 .
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