title: Target analysis studies of red cell water and urea transport.
abstract: Radiation inactivation was used to determine the nature and molecular weight of water and urea transporters in the human red cell. Red cells were frozen to -50 degrees C in a cryoprotectant solution, irradiated with 1.5 MeV electrons, thawed, washed and assayed for osmotic water and urea permeability by stopped-flow light scattering. The freezing and thawing process did not affect the rates of water or urea transport or the inhibitory potency of p-chloromercuribenzenesulfonate (pCMBS) on water transport and of phloretin on urea transport. Red cell urea transport inactivated with radiation (0-4 Mrad) with a single target size of 469 +/- 36 kDa. 40 microM phloretin inhibited urea flux by approx. 50% at each radiation dose, indicating that urea transporters surviving radiation were inhibitable. Water transport did not inactivate with radiation; however, the inhibitory potency of 2.5 mM pCMBS decreased from 86 +/- 1% to 4 +/- 9% over a 0-2 Mrad dose range. These studies suggest that red cell water transport either required one or more low-molecular-weight proteins, or is lipid-mediated, and that the pCMBS-binding site which regulates water flow inactivates with radiation. These results also suggest that red cell urea transport is mediated by a specific, high-molecular-weight protein. These results do not support the hypothesis that a band 3 dimer (190 kDa) mediates red cell osmotic water and urea transport.
mesh_terms: D002731:4-Chloromercuribenzenesulfonate / Q000494:pharmacology; D001693:Biological Transport, Active / Q000187:drug effects / Q000528:radiation effects; D002463:Cell Membrane Permeability; D004058:Diffusion; D004307:Dose-Response Relationship, Radiation; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D005615:Freezing; D006801:Humans; D008433:Mathematics; D008970:Molecular Weight; D009995:Osmosis / Q000528:radiation effects; D010693:Phloretin / Q000494:pharmacology; D014508:Urea / Q000378:metabolism*; D014867:Water / Q000378:metabolism*
chemical_list: D014867:Water; D002731:4-Chloromercuribenzenesulfonate; D014508:Urea; D010693:Phloretin