ISSN:
1432-1424
Schlagwort(e):
diffusive water permeability
;
kidney tubules
;
water channels
;
epithelia
;
nuclear magnetic resonance (NMR)
;
single-file diffusion
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Biologie
,
Chemie und Pharmazie
Notizen:
Summary The diffusive water permeability (P d ) of the plasma membrane of proximal kidney tubule cells was measured using a1H-NMR technique. The values obtained for the exchange time (T ex) across the membrane were independent of the cytocrit and of the Mn2+ concentration (in the range 2.5 to 5mm). At 25°C the calculatedP d value was (per cm2 of outer surface area without taking into account membrane invaginations) 197±17 μm/sec. This value equals 22.3±1.9 μm/sec when the invaginations are taken into account. Cell exposure to 2.5mm parachloromercuribenzenesulfonic acid,pCMBS, (for 20 to 35 min) reducedP d to 45% of its control value. Fivemm dithiothreitol, DTT, reverted this effect. The activation energy for the diffusive water flux was 5.2±1.0 kcal/mol under control conditions. It increased to 9.1±2.2 kcal/mol in the presence of 2.5mm pCMBS. Using our previous values for the osmotic water permeability (P os) in proximal straight tubular cells theP os/P d ratio equals 18±1, under control conditions, and 3.2±0.3 in the presence ofpCMBS. These experimental results indicate the presence of pathways for water, formed by proteins, crossing these membranes, which are closed bypCMBS. Assuming laminar flow (within the pore), fromP os/P d of 13 to 18 an unreasonably large pore radius of 12 to 15 Å is calculated which would not hinder cell entry of known extracellular markers. Alternatively, for a single-file pore, 11 to 20 would be the number of water molecules which would be in tandem inside the pore. The water permeability remaining in the presence ofpCMBS indicates water permeation through the lipid bilayer. There are similarities between these results and those obtained in human red blood cells and in the apical cell membrane of the toad urinary bladder.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF01871900
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