Red Cell Size and Resistance to Osmotic Hemolysis

Abstract

In explanation of the fact that the red cells of different mammals show different “fragilities”, i. e., different resistances to osmotic hemolysis, it has been pointed out that the extent dA to which the least resistant cell membrane can be stretched without there being a loss of pigment depends on the mean initial cell volume V, so that the ratio dA/V is substantially constant. This purely experimental result can be interpreted as meaning that molecules adjacent to the thin (perhaps bi-molecular) layer upon which semi-permeability depends can enter it when it is stretched, thereby allowing of a certain amount of stretching before lysis occurs (Ponder 1 ).∗ Another well known fact is that different red cells of the same animal show different “fragilities”, so that a resistance distribution of roughly symmetrical form arises with respect to tonicity. One would expect that here too the resistance might be related to the initial cell volume, and it is with this point that this note is concerned.

The volume which any cell of initial volume V_o reaches in a hypotonic solution of tonicity T is

V and V_o being both measured in μ³. In this expression W is the amount of water contained in the cell, expressed as a percentage by volume, and R is a constant which measures either the fraction of the total cell water which is “solvent water” (the view of Parpart and Shull 2 ), or the extent to which the cell behaves as a “perfect osmo-meter” (the view of Ponder and Saslow 3 ). The expression supposes that the volume of the hypotonic solution surrounding the cells is very great as compared with the volume of the cell water, as it usually is in fragility experiments. Supposing that the cell hemolyses when V reaches the critical volume V_o; then, if the stretching of the cell membrane is proportional to the initial volume V_o, we have hemolysis when

Here the value 0.207 is that of 1/(0.75 π)^2/3 4π and the constant K is the constant in the expression dA = KV_o which expresses the experimental result that the amount of stretching which a given cell can undergo is proportional to the initial volume V_o.