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B Chasan

Publications and source records attributed to B Chasan.

3 recordsLinked to original sources
PubMed1985

Urea reflection coefficient for the human red cell membrane.

The reflection coefficient, sigma, is an irreversible thermodynamic parameter which measures the interaction between solute and solvent in passage across a membrane. The initial estimate of Goldstein and Solomon ((1960) J. Gen. Physiol. 44, 1-17) by the zero-time method gave sigma urea = 0.6 for the human red cell membrane and a more recent measurement by Levitt and Mlekoday ((1983) J. Gen. Physiol. 81, 239-253) using a different method gave sigma urea = 0.95. We have now developed a variant of the zero-time method which gives sigma urea = 0.70 +/- 0.02, which is significantly different from 1.0. There has been controversy as to whether urea permeates the human red cell by the same channel used by water or by a different route. The finding that sigma urea is significantly less than 1.0 (actually less than 0.95) makes it possible to discriminate between these two possibilities since completely independent transfer of urea and water mandates a value of sigma urea = 0.95. Values significantly lower than 0.95 can only be achieved if the transport of the solute, urea, is coupled to that of the solvent, water.

Adult↗
PubMed1984

Effect of thiourea on PCMBS inhibition of osmotic water transport in human red cells.

The organomercurial reagent p-chloromercuribenzene sulfonate (PCMBS) is an inhibitor of osmotic water permeability in the human red cell membrane. We have found that thiourea, when added along with PCMBS to a red cell suspension, interferes with this inhibition and at high enough concentrations prevents the inhibition from developing altogether. For a 2 mM PCMBS concentration Ki = 3 +/- 1 mM. When thiourea is added at a later time, the PCMBS inhibition, which normally takes about 20 min to develop fully, is halted and remains fixed at the value attained by that time. Thiourea also inhibits the reversal of PCMBS inhibition by a 10 mM concentration of cysteine, the half-time for reversal increasing by more than an order of magnitude when [thiourea] = 50 mM. Possible implications for the nature of the water and urea transport pathways across the red cell membrane are discussed.

4-Chloromercuribenzenesulfonate↗