Osmotic permeability of Novikoff hepatoma cells

Water permeability of isolated endothelial cells at different temperatures

The endothelial cells provide a potential pathway for water movement across the endothelium. The endothelial cell permeability to water can, therefore, be a factor in regulation of the rate of water movement out of the vasculature. Endothelial cells are isolated from calf pulmonary artery and cultured. The cells are removed from culture, and the diffusional water permeability is determined with the linear diffusion technique. The mean membrane permeability coefficients (PDS) determined at 20, 30, 37, and 41 degrees C are 160, 273, 304, and 387 x 10(-5) cm/s, respectively. The temperature dependence of PD is calculated with the Arrhenius equation to be 7.2 kcal/mol. If these values of PD are compared with values we have reported for the osmotic permeability coefficient (PF), the PF/PD is about one at each temperature. The values of PD in the isolated endothelial cells are compared with PD for endothelial cells estimated from whole organ studies and are similar to recently reported values.

The osmotic permeability of isolated calf pulmonary artery endothelial cells

Osmotic permeability coefficients, PF, for water in isolated calf pulmonary artery endothelial cells determined over the temperature range 41 to 20 degrees C are 311.10(-5) cm.s-1 at 37 degrees C and 159.10(-5) cm.s-1 at 20 degrees C. The value at 37 degrees C is close to that reported earlier for the diffusional permeability coefficient, PD. The PF/PD ratio is 1.0 at 37 degrees C. The PF values are within the range of values extrapolated for filtration permeability in pulmonary endothelium. The temperature dependence expressed as the activation energy is 7.2 kcal.mol-1. The product of hydraulic conductivity, Lp (or PF) and of viscosity changes in water is not constant from 37 to 20 degrees C. These results can be interpreted to indicate a similar pathway for water whether under diffusional or osmotic gradients.

Water permeability of alveolar macrophages

The hydraulic conductivity coefficient (Lp) of alveolar macrophages, recovered by lavage from dog lungs, was determined by following volume changes induced by changes of nonpermeating solute concentrations of suspending fluid as a function of time at 20 degrees C. The volume changes were monitored as changes in absorbance of the suspended cells at 600 nm. Cell surface area was calculated from cell volume and diameter. Linear relationships between cell volume and solution osmolality changes were found over the range of 320-520 mosmol/kg; beyond these ranges the macrophages did not respond with swelling or shrinking. Lp and the filtration coefficient (Pf) were calculated from the total volume change over time. At 20 degrees C these were, respectively, 15.7 X 10(-10) cm X cmH2O-1 X s-1 and 217 X 10(-5) cm/s. Comparison of Pf and the diffusional permeability coefficient (Pd) for water of 70 X 10(-5) cm/s, yields a Pf-to-Pd ratio of 3.1. The hypothesis of water passage through aqueous membrane pores is compatible with these data. However, diffusion of water in the glycocalyx of the pericellular domain could be restricted. Pd would then be underestimated, and a falsely high ratio would be calculated. We have no evidence to support this possibility.

Solute-excluded volumes near the Novikoff cell surface

A differential centrifugation technique, in which all extracellular water except that intimately associated with the cell (pericellular domain) is removed, has been applied to isolated Novikoff hepatoma cells. The pericellular volumes accessible to albumin, inulin, raffinose, and sucrose were inversely related to the molecular weights of the test solutes. This phenomenon was not detectable in erythrocytes or in fat cells. Selective removal of cell surface components by enzymatic treatment produced proportional changes in the relative volumes of distribution accessible to the solutes. This discrimination in the volume accessible to each of the solutes is analogous to that obtained in gel chromatographic separation and represents, in effect, excluded volumes which are inversely related to solute size. This exclusion is associated with components of the Novikoff cell surface, including the surface coat and the microvilli that cover the Novikoff cell. These structures provide an additional level of discrimination for the Novikoff cell not seen in certain other cell types.

Water permeability through biological membranes by isotopic effects of fluorescence and light scattering

A light-scattering technique used to measure the water permeability across closed biomembranes is described, which is based on the different indices of refraction of D2O and H2O. This transient technique is compared with a similar method using D2O-sensitive fluorophores in the intravesicular space. The results of both techniques are equivalent although the signal-to-noise ratio favors the light-scattering or turbidity experiment. The light-scattering method is only applicable to larger particles (no point-scatterers) and is easily extended to biological objects. Data on the H2O/D2O exchange across membranes of ghosts from human erythrocytes suggest two mechanisms: the D2O and H2O permeation through the membrane and a slower D2O-induced conformational change of membraneous proteins.

Permeability of Novikoff hepatoma cells to water and monohydric alcohols

The permeability coefficients of Novikoff hepatoma ascites cell membranes for tritiated water (3HHO) and for a homologous series of monohydric alcohols (methanol through hexanol) were deduced from linear diffusion coefficients by means of a series-parallel pathway model (Redwood et al. (1974) J. Gen. Physiol. 64, 706-729). Membrane permeability coefficients for 3HHO at 20, 30 and 37 degrees C were (all x 10(-5)) 97, 125, and 163 cm . s-1, respectively, and were significantly smaller than the corresponding values for the alcohols tested. In the alcohols series, ethanol had the lowest permeability coefficient 198 x 10(-5) cm . s-1 at 20 degrees C. The apparent activation energy for water permeation was 6.7 +/- 1.9 S.E. kcal . mol-1. The apparent membrane diffusion coefficients for the alcohols were a complex function of molecular properties with less diffusional membrane resistance to the alcohols in the middle of the homologous series than would have been expected on the basis of oil-water partitioning or molar volume considerations. The conventional parallel aqueous lipophilic pathway model is not consistent with the present data which can be interpreted by consideration of parallel lipophilic pathways through the Novikoff hepatoma cell membrane.