. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. INTAKE OF IONS BY MARINE EGGS 221 Both were done before the realization that erythritol solution washing was remov- ing the ions to a great extent. The closest approximation made on the basis of the rate of intake of these ions in the first 2 or 4 minutes, corresponding to the first peak, has been made on Experiment 5, not here otherwise shown. The rates of intake were sodium: X 10~8; phosphate: X 10~8 moles cm~2 hr"1. Compensating for the different concentrations used we obtain permeability con- stants for so
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. INTAKE OF IONS BY MARINE EGGS 221 Both were done before the realization that erythritol solution washing was remov- ing the ions to a great extent. The closest approximation made on the basis of the rate of intake of these ions in the first 2 or 4 minutes, corresponding to the first peak, has been made on Experiment 5, not here otherwise shown. The rates of intake were sodium: X 10~8; phosphate: X 10~8 moles cm~2 hr"1. Compensating for the different concentrations used we obtain permeability con- stants for sodium: X 1Q-6; phosphate: X 1Q-6 moles cm~2 hr"1" (GM L"1)"1- It appears possible that the sodium cation penetrates about 17 times as easily as the phosphate dianion. Too many considerations enter into this picture to allow drawing conclusive values. For example, the mobility of phosphate calculated from conductivity, diffusion, etc. is between those of K+ and Na+, the equivalent conductivity of 3/2 HPO4= is 57 while K+ and Na+ show and This would be expected from the dimensions (Figure 6) of hydrated K+ (1H2), Na+ (7 H2O) and HPO4= HPO. FIGURE 6. The van der Waals volumes of sodium (Na+), potassium (K+), and phosphate (HPO4=) ions, drawn to scale, with the mean number of water molecules attached to them in moderately concentrated aqueous solution. An ion approaching a plasma membrane would carry this hydration. Removal of this water (which may be necessary for passage) requires expenditure of work. (unhydrated); whereas the deduction from Figure 5 would require hydration of HPO4= presumably about 3 H2O to account for the lower penetrability of this ion. This envisages a plasma membrane structure which will act as an ultrafilter whose available (existent or potential) free spaces are about 7-9 A in diameter. This corresponds generally with the results with chiefly water soluble substances, but different cells or tissues seem to vary c
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