The Internal Viscosity of the Red Cell and the Structure of the Red Cell Membrane. Considerations of the Liquid Crystalline Structure of the Red Cell Interior and Membrane from Rheological Data

Abstract

Abstract In a series of experimental studies, carried out by means of rotational and microcapillary viscometers, it was possible to show that the viscosity of packed human cells, at haematocrits up to 98 per cent, is in the range from 10 to 1,000,000 centipoises, depending on the shear rate and on the type of the red cell (i.e., the normal red cell, the sickle cell, crenated cells, etc.). The viscosity of blood, or of suspensions of the red cells, is also very low and requires an acceptance of the red cell as a (complex) fluid drop. A study of suspensions of red cells in the continuous phases of different viscosities (i.e., blood plasma, saline, dextrane solutions) and osmolalities confirms that the internal viscosity of the red cell must be very low indeed. An equation, which is based on the Roscoe, Brinkman and Taylor equations, and which reduces at low concentrations to Taylor's equation, is applied in order to define the internal viscosity of the red cell. This is found to be between 1 and 6 centipoises for the normal cells and up to 20 or more centipoises for the abnormal red cells. These values include the contribution of the redcell membrane. Utilizing equations of Oldroyd and Boussinesq, the surface viscosity of the red cell is estimated to be between 0.000001 and 0.000004 surface poises. An attempt is made to reconcile these values with the data of Katchalsky and Burton and Band. Such reconciliation is feasible if the viscosity of the membrane is very high at high stresses and/or during haemolysis; and if the elastic modulus is also proportional, in some manner, to the stresses applied. It is suggested that the membrane is of thixotropic-dilatant type with a non-Hookean elastic component; a non-linear viscoelastic body which is time-dependent. A molecular structure of such membrane could be composed of two main phases: one which would be liquid crystalline, and the second which would be formed of a loose and dynamic network of proteins. A multiphase, complex, dynamic, heterogeneous and liquid crystalline membrane would be compatible with the current ideas on the structure of biological membranes, on the active transport and on the catalytic reactions within the cell membrane.