Osmolality effects in neurons: I. permeability coefficient and a model of water flux

The rate of swelling of Aplysia neurons has been measured in hypo-osmolal solutions and from this the osmotic permeability coefficient has been calculated to be P w ≅ 35 x 10 -7 ml/cm 2 /sec/osmole/liter difference across the plasma membrane. Considering nine different forms of H-bonded water structure, each with a different concentration and energy, a random walk model of osmotic water flux through a single plasma membrane pore of molecular dimensions has been developed. This provides an order-of-magnitude expression for osmotic water flux, J ≅ 8.9 x 10 -18 ml/sec/osmole/liter difference through a single pore. By combining P w and J , we obtain an estimate of the number of pores per square centimeter of membrane N p ; N p = P w J≅4 × 10 11 pores/cm 2 . If we assume a rectangular arrangement of pores with equal spacing, this gives an order of magnitude approximation of 160 A between pore centers.