THE DIFFUSIONAL TRANSPORT OF WATER AND SMALL SOLUTES IN ISOLATED ENDOTHELIAL-CELLS AND ERYTHROCYTES

The diffusional permeability coefficients, P(D), for tritiated water ((HHO)-H-3) C-14-antipyrine (AP) and C-14-iodoantipyrine (IAP) in isolated calf pulmonary artery endothelial cells and dog erythrocytes are measured with the linear diffusion technique at 11.5, 15, 20 and 37-degrees-C. The P(D) values for both cell populations follow the sequence (HHO)-H-3 > IAP > AP at each of the temperatures. P(D) for water is higher in the erythrocyte compared to the endothelial cells. The differences in P(D) for AP and IAP in the erythrocytes and endothelial cells are not dramatic and are similar to the differences seen in comparing permeation of the same solute through bilayers of different composition. A comparison of the values of P(D) calculated for the endothelial cells with those for isolated capillaries and the structured endothelium in whole lungs validates the use of the isolated cells as models for the endothelial cells in situ. Incubation of the endothelial cells with cis-vaccenic acid or cholesterol produces a reduction in P(D) for water and antipyrine. These data are analyzed in terms of Stokesian and non-Stokesian diffusion. The interpretation which best accommodates the data is that the phospholipid area of the membrane, rather than the hydrocarbon core, provides the greatest resistance to permeation for these solutes.