Red Cell Membrane Structure and Ion Transport

The red cell in man is a biconcave disk, some 8.4/z in diameter, 2.4 # thick at its widest portion, and 1/z thick at its narrowest. It is bounded by a membrane primarily composed of protein and lipid, the latter sufficient in amount to cover the red cell with a layer two molecules thick. The lipid layer is bounded on the outside, and possibly on the inside, by a layer of protein. The thickness of the membrane is not known accurately since the most reliable studies, those made with the electron microscope and by optical refraction, are necessarily made with dried material. The best estimates of membrane thickness lead to values of the order of 100/~. Within the human red cell, there is a high K concentration, 143 mu/liter cell water, and a low Na concentration, 13.9 rn~/liter cell water. In the environment, the situation is reversed, since plasma contains 5.0 mM K and 154 mM Na/liter plasma water (1-3). The present paper is concerned with the role of the cellular membrane in the creation and maintenance of these sharp differences in ionic composition across a barrier that is only a few molecules thick, a problem common to a wide variety of living cells. The conclusions are based on studies carried out in this laboratory in company with a number of associates,