ION EFFECTS UPON ION PERMEABILITY OF THE FUNDULUS CHORION

¹ From the Marine Biological Laboratory, Woods Hole, and the Department of Physiology, University of Pennsylvania Medical School

By additional measurements of concentration potential differences across the chorion of single Fundulus eggs, certain suggestions made in an earlier paper have been confirmed and amplified. In acid-free solutions of KCl, CaCl₂, and K₂SO₄ the chorion was found more freely permeable for positive ions than for negative. Its preferential permeability for cations was reduced in all three salts by increasing acidity. In the first two, it was abolished and then reversed, the pH at which equal permeability for anions and cations was reached being about 3.5 in KCl, and 3.9 in CaCl₂. In K₂SO₄, however, reversal did not occur down to pH 2.0.

The results suggest an explanation for the mechanism of salt antagonisms for acid penetration into Fundulus eggs, a somewhat practical problem. And, from a theoretical standpoint, they seem to furnish evidence that membrane potentials are fundamentally related to diffusion potentials.