Electrolytes control flows of water and sucrose through collagen membranes

Abstract

Summary. The physical state of a collagen membrane is determined, among other factors, by the concentration of electrolytes in the bathing solutions, going from a crystalline to an amorphous phase as the concentration increases. Thus, the permeation of uncharged solutes and water is strongly dependent upon the salts in the bathing solutions, which through the induced phase transition control not only the thickness and the solvent content of the membrane but also affect the magnitudes of the frictional coefficients of transport. These changes in physical parameters are reflected in variations of several hundred per cent in the values of the phenomenological coefficients o~s, Lp and tr. Experiments were performed to determine the physical state and the permeability properties of the membrane as functions of the controlling electrolyte, in this instance CaCI2, in the bathing solutions. In particular the filtration coefficient Lp, the permeability coefficient for sucrose co s, and the reflection coefficient for sucrose tr were determined via flow measurements at different salt concentrations. Complementary measurements of swelling and length variations were made. Data were reduced to membrane thickness, solvent volume-fraction, and the phenomenological coefficients. These in turn were reduced to the frictions fsm, fsw and fwm; there was a direct correlation between the behavior of these frictions and the physical state of the collagen membrane as indicated by the length and volume variations.The magnitudes of the flows of uncharged solutes and water through a simple collagen membrane are controlled by the concentration of electrolytes in the bathing solutions. Significant variations in the permeabilities of the order of several hundred per cent are caused primarily by phase changes in the membrane matrix, the collagen molecules going from a crystalline helix conformation to an amorphous random-coil conformation as the elec-* Thesis presented at the Institute of Physics of the University of Genoa, Italy as a partial requirement for the degree in physics.

Electrolytes control flows of water across the apical barrier in toad skin: The hydrosmotic salt effect

“…10) indicates that the mechanism of increasing water permeability is not due to incorporation of new water permeability units into the apical border of the most superficial epithelial cells but is due to modification of existing water pathways in this structure. In artificial collagen membranes, it has been shown that permeability to solutes and water is strongly dependent upon the salt concentration of bathing solution (Bartolini, Gliozzi & Richardson, 1973), and this behavior is due to membrane phase transitions. In our case, it is also possible that membrane proteins change their configuration as a function of external bathing solution ionic strength.…”

Hydrosmotic salt effect in toad skin: Urea permeability and glutaraldehyde fixation of water channels

“…These differences support the hypothesis that the increase * Present address: Escola Paulista de Medicina, Department of Biophysics. in water permeability in the course of the HSE is not due to incorporation of new water permeability units, or channels, into the apical border of the most superficial epithelial cells, as accepted for the ADH effect [8,9,18], but seems to be due to modification of existing structures leading to the opening of water pathways [5]. In artificial collagen membranes, the permeability to solutes and water is strongly influenced by the ionic strength of the bathing solution, and this effect is mediated by membrane phase transition [4].…”