Why Red Cells?

Abstract

This is a book about the passage of matter across the plasma membrane of the mature and, for the most part, nonnucleated red blood cell (of mammals). It seems appropriate at the outset to try to answer the question of why one wishes to know much about such processes (although the reader certainly has his or her own answer). The textbook truth is that the only obvious function of mature red cells in the body’s economy is to transport oxygen (why it is advantageous to have haemoglobin within a membrane-bounded space rather than in free solution must not concern us here). Yet, necessarily, there is a red-cell membrane. In point of fact, there is too much of it for the volume of the cell. Human red cells can swell by about 50 per cent (increasing their water content by 70 per cent) before reaching the volume of a sphere having the surface of the original disc. Since water-permeable bags filled with a 5 mM protein solution will swell and eventually burst by colloid-osmotic lysis, keeping water out of the cell is a vital function of the plasma membrane. On aging in the circulation, red cells do not swell but become even further dehydrated (and therefore heavier). Lew and Bookchin (1986) offer an astute explanation for this all but self-evident fact.