Erythrocytes water permeability

Sukul NC, De A, Sinhababu SP, Sukul A. 2003. Potentized Mercuric chloride and Nux vomica facilitate water permeability in erythrocytes of a freshwater catfish Clarius batrachus under acute ethanol intoxication. J Alt Comp Med 9 719-725. 

The presence of water channels has been demonstrated by successful cloning of proteins that increase membrane water permeability. These have been expressed in erythrocytes and in cells of the renal tubule. 

The effects of temperature on the distribution of non-electrolytes between erythrocytes and the surrounding medium in vitro has been investigated with H NMR. The results indicated that between 4° and 37° the rate of uptake by erythrocytes was a function of temperature. The inhibition of water-permeability by diffusion (P ) through the erythrocyte membrane has been investigated using NMR. Maximal inhibition of 50% of Pd was achieved by 2 mM -chloromercuri benzoate in 20 min. The maximal effect of />-chloro-mercuri benzoate was reduced by the presence of lipophilic solutes. However, lipophilic solutes alone caused a faster inhibition of Pd, though this was less efficient than that from p-chloromercuri benzoate. A method has been developed to observe early phosphate penetration into erythrocytes. When the main extracellular cation was Na, 100 mM extracellular Pi penetrated the cells within one hour. When the main extracellular cation was the apparent penetration rate of Pi was reduced by 25%. The influx of Pi into erythrocytes was not accompanied by a change in pHj. ... 

The importance of lipids in membrane structure was established early in the 20th century when pioneering biophysicists established positive correlations between cell membrane permeabilities to small non-electrolytes and the oil/water partition coefficients of these molecules. Contemporary measurements of the electrical impedance of cell suspensions suggested that cells are surrounded by a hydrocarbon barrier, which was first estimated to be about 3.3 nm thick. This was originally thought to be a lipid monolayer. Among the pioneering biophysical experiments were those that established that the ratio of the area of a monolayer formed from erythrocyte... 

Gryns (1896), Hedin (1897), and especially Overton (1900) looked at the permeability of a wide range of different compounds, particularly non-electrolytes, and showed that rates of penetration of solutes into erythrocytes increased with their lipid solubility. Overton correlated the rate of penetration of the solute with its partition coefficient between water and olive oil, which he took as a model for membrane composition. Some water-soluble molecules, particularly urea, entered erythrocytes faster than could be attributed to their lipid solubility—observations leading to the concept of pores, or discontinuities in the membrane which allowed water-soluble molecules to penetrate. The need to postulate the existence of pores offered the first hint of a mosaic structure for the membrane. Jacobs (1932) and Huber and Orskov (1933) put results from the early permeability studies onto a quantitative basis and concluded molecular size was a factor in the rate of solute translocation. 

Aquaporins (AQPs) are a family of at least 13 members of small membrane-spanning proteins that assemble in cell membranes as homotetramers (Verkman and Mitra, 2000 Agre et al 2002 Verkman, 2005). Each monomer is approximately 30 kDa and six a-helical domains with cytosolically oriented amino- and carboxy-termini surround the water pore (Verkman and Mitra, 2000). AQPs can transport water in both directions (Tail et al., 2008). Early experiments demonstrating that erythrocyte membranes are more permeable to water than expected from water diffusion through a lipid bilayer provided the first experimental evidence of the existence of AQPs (Sidel and Solomon, 1957). 

The walls of erythrocytes (red blood cells) are permeable to water. In a salt solution, they shrivel (lose water) when the outside salt concentration is high and swell (take up water) when the outside salt concentration is low. In an experiment at 25°C, an aqueous solution of NaCl that has a freezing point of 0.406°C causes erythrocytes neither to swell nor to shrink, indicating that the osmotic pressure of their contents is equal to that of the NaCl solution. Calculate the osmotic pressure of the solution inside the erythrocytes under these conditions, assuming that its molarity and molality are equal. 

All of the authors imply that separation of water phases probably occurs at the cellular level. The semi-permeable nature of the cell membrane towards ions and solutes which are capable of relaxing water protons provides compartments in which relaxation rates can be significantly different, even when water transport across the membrane is very rapid. Indeed this property of whole tissue has been used in the development of an NMR method of determining water transport across erythrocyte membranes (11). 

Fig. 4 depicts the data of Sha afi et al. [11], of Savitz and Solomon (12) and of Klocke et al. [13] on the penetration of 23 different compounds into human red cells plotted as a log/log plot (cf. Fig. 1) against the relevant ether/water partition coefficient. The strong dependence of permeability on partition coefficient that was noted by Collander for plant cells is somewhat less obvious for the human erythrocyte. Values of the partition coefficient vary over a range of 10 for molecules which have the same permeation rate. Molecules with the same partition coefficient have permeation rates which vary over a range of 10. But a line of unit slope can be drawn through many of the points on the log/log plot showing the strong dependence of permeation coefficients on partition coefficients. 

The cytoplasmic membrane of an erythrocyte or a comeal epithelial cell and other physiological membranes, however, do not always behave as a semi-permeable membrane. Cell membranes are to some extent also permeable to some molecules other than water. Some molecules or ions, such as urea, ethanol, and ammonium salts, are able to pass... 

This is important for permeability, since plasma membranes appear to contain a high proportion of lipides, as shown, e.gr., for erythrocytes by Dziemian (18). Ethylene would be able, by virtue of its apolar structure, to dissolve in the lipide phase and to counteract the bonding effect of the double bonds of the lipide hydrocarbon chains. At first, however, the presence of additional apolar molecules may account for the frequently observed decrease in permeability, while the ultimate invasion of the membrane by ethylene would disrupt it, with increased permeability. This permeability is here thought of as applying to glucose and other molecules highly soluble in water. 

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