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Urea reflection coefficient for the human red cell membrane.

B Chasan, A K Solomon

    Biochimica Et Biophysica Acta
    |November 21, 1985
    PubMed
    Summary
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    This study refines the measurement of urea

    Area of Science:

    • Membrane biophysics
    • Physical chemistry
    • Human physiology

    Background:

    • The reflection coefficient (sigma) quantifies solute-solvent interactions during membrane transport.
    • Previous estimates for urea's reflection coefficient (sigma urea) across human red cells varied significantly (0.6 to 0.95).
    • Understanding urea transport is crucial for human red cell physiology.

    Purpose of the Study:

    • To develop a refined method for measuring the reflection coefficient of urea across the human red cell membrane.
    • To resolve discrepancies in previous sigma urea measurements.
    • To elucidate the transport mechanism of urea in human red cells.

    Main Methods:

    • A modified zero-time method was employed to measure the reflection coefficient.

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  • This technique assesses the interaction between solute (urea) and solvent (water) passage across the membrane.
  • Measurements were specifically conducted on human red cell membranes.

    • Main Results:

    • The study determined a new value for sigma urea of 0.70 +/- 0.02.
    • This result is significantly different from 1.0 and also distinct from the previously reported 0.95.
    • The obtained sigma urea value is significantly less than 0.95.

    Conclusions:

    • The finding that sigma urea is significantly less than 0.95 suggests urea transport is coupled to water transport.
    • This contrasts with completely independent transfer, which would yield sigma urea = 0.95.
    • The results indicate that urea likely does not use a separate channel from water but shares a common pathway or exhibits coupled transport.