Cell osmotic water permeability of isolated rabbit proximal convoluted tubules

Cell osmotic water permeability, Pcos, of the peritubular aspect of the proximal convoluted tubule (PCT) was measured from the time course of cell volume changes subsequent to the sudden imposition of an osmotic gradient, delta Cio, across the cell membrane of PCT that had been dissected and mounted in a chamber. The possibilities of artifact were minimized. The bath was vigorously stirred, the solutions could be 95% changed within 0.1 s, and small osmotic gradients (10-20 mosM) were used. Thus, the osmotically induced water flow was a linear function of delta Cio and the effect of the 70-microns-thick unstirred layers was negligible. In addition, data were extrapolated to delta Cio = 0. Pcos for PCT was 41.6 (+/- 3.5) X 10(-4) cm3 X s-1 X osM-1 per cm2 of peritubular basal area. The standing gradient osmotic theory for transcellular osmosis is incompatible with this value. Published values for Pcos of PST are 25.1 X 10(-4), and for the transepithelial permeability Peos values are 64 X 10(-4) for PCT and 94 X 10(-4) for PST, in the same units. These results indicate that there is room for paracellular water flow in both nephron segments and that the magnitude of the transcellular and paracellular water flows may vary from one segment of the proximal tubule to another.

Cell wall elastic properties of Chara corallina

Transcellular osmosis measurements are combined with measurements of the kinetics of relative length change, when Chara corallina cells are transferred from artificial pond water to polyethylene glycol (mol wt 300 to 400) of higher osmotic pressure to yield the constant k, which relates relative volume change ΔV/V to relative length change Δl/l (ΔV/V = k Δl/l). The value of k is 3.5 and is temperature independent between 7 and 30 °C. Static and kinetic estimates of the bulk modulus, ε, indicate that ε is temperature independent and has a value between 500 to 650 bars at high turgor pressures. The value of ε declines as the turgor pressure declines. We show how ε and k are related to Young's modulus and to Poisson's ratio for anisotropic C. corallina cell walls and point out that the previous treatments of the problem are in error.

Note on lack of effect of ethylene on water permeability, electroosmotic efficiency, or transcellular water flow of the plasma membranes in Nitella

Ethylene (4.0 mM) in artificial pond water had no significant effect on three permeation properties of the plasma membranes of Nitella 2 h after addition. Neither the hydraulic permeability measured by transcellular osmosis, the passive monovalent cation permeability measured by electroosmosis, nor the 'active' transcellular water flows were altered appreciably by ethylene in solution.

The effect of pH and ABA on the hydraulic conductivity of Nitella membranes

The method of transcellular osmosis was used to compare the hydraulic permeability (LP) of Nitella membranes at different pH's. LP did not change when the pH ranged from 5.0 to 7.0 but dropped slightly when the pH was 4.4 or below. Tris(hydroxymethyl)aminomethane buffer and abscissic acid (ABA) both increased LP significantly.

Water Permeability of a Characean Internodal Cell with Special Reference to Its Polarity

Water permeability (hydraulic conductivity) of the Nitella internode was studied by means of transcellular osmosis with special reference to its polarity. It was shown that the change in turgor or in cell volume involved in transcellular osmosis is ahnost over within 5 sec after the onset of both forward and backward osmoses. What is different with respect to turgor between the two osmoses is its final level. In forward osmosis the turgor drops down to a definite level depending on the external concentration, while in backward osmosis the turgor invariably comes back to the normal level.