The failure of hydrodynamic analysis to define pore size in cell membranes.

The equivalent pore theory predicts that the size of water transporting pores can be calculated from the ratio of osmotic (Pf, cm . s-1) to diffusive (Pd, cm . s-1) water permeability. Determinations of Pf and Pd in human red cells within the last thirty years have increased the ratio of Pf to Pd. According to the equivalent pore theory the pore diameter has increased from 9 A to 25 A. A pore diameter of 25 A is not compatible with the permeability characteristics of the red cell membrane. We conclude that the equivalent pore theory fails to determine pore size in red blood cells. We suggest that water transporting pores in human red cells transport water molecules in a single file fashion.