Osmotic properties of differentiating bone marrow precursor cells: Membrane permeability to non-electrolytes

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Abstract
Membrane permeability to the non‐electrolyte probes urea and thiourea was measured in a population of differentiating bone marrow precursor cells (Cicoria and Hempling, '80). The phenomenologic equations of Kedem and Katchalsky ('58) were applied. The population of cells, which can be separated by velocity sedimentation, was examined over the maturation range of 400 to 1,000 cubic micra. Several membrane properties were observed: (1) Solute permeability (R̃) increased linearly as the cell volume increased, while the reflection coefficients (σ) remained constant. (2) Membrane permeability to urea was significantly greater than to thiourea; however, their respective sigmas did not differ significantly. Solute permeability was independent of sigma at 22 degrees C. (3) In the two maturation phases observed, wr̃ varied directly with the volume of osmotically active water. (4) The permeability to urea and to thiourea has provided information on the characteristics of the pathways used for water and non‐electrolytes, as well as a description of the phenomenologic membrane events accompanying cellular maturation.