Permeability of Red Corpuscles of the Dog to Sodium Ion. ∗

The question of the permeability of mammalian erythrocytes to cations (with the exception of hydrogen ion) has long been a controversial one. The literature in the field has been reviewed by Ponder 1 and Jacobs. 2 Ponder states that, although there has been some evidence since 1891 3 that the red blood cell is permeable to cations, it has generally been assumed that it is not. 4 Such an assumption requires awkward corrections to explain the experimental data. To avoid postulating a cation shift across the red cell membrane, Ponder 1 states that Van Slyke and Cullen, 5 Mellanby and Wood, 6 and Doisy and Eaton 7 have preferred to introduce corrections involving changes in red cell volume. However, Van Slyke and Cullen 5 admit the possibility of a transfer of cations between plasma and corpuscles. For these volume changes, which are ascribed to water shifts, there is no good evidence, the most careful work giving results varying by as much as 100% 8 or even varying in direction. 9 Much of the interpretation is based on hematocrit values which are admittedly unreliable. If there is no water shift, or if it is not of the right magnitude, the results of the investigators mentioned above support the idea of a red blood cell permeable to cations.

Jacobs, 2 on the basis of Donnan ratios, relation of cell volume to osmotic pressure, and volume changes in solutions of varying pH (with CO₂), concludes that the red blood cell is impermeable to cations. As Ponder 1 has pointed out, the evidence is inconclusive on all 3 points, and Jacobs himself admits the possibility of alternate explanations.