Multiple Partition Coefficients of Penetration.

Abstract

Overton's lipoid theory 1 which states that only dyes soluble in lipoid can penetrate into living cells, is inadequate in certain respects. 2 This is due in part to the fact that he considered only one partition coefficient, that of the dye between the external solution and the lipoid layer surrounding the living cell. Since it is chiefly cytoplasmic inclusions, granules, fat globules, vacuoles, etc., which are stained rather than the cytoplasm proper, it is necessary to consider several partition coefficients, such as: (1) That of the dye between the non-aqueous layer surrounding the cytoplasm and the external solution. (2) That of the dye between the same nonaqueous layer and the aqueous cytoplasm. (3) That of the dye between the aqueous cytoplasm and the inner non-aqueous inclusions (granules, or fat globules) or the non-aqueous layer surrounding the vacuole. (4) That of the dye between the inner non-aqueous layer of the vacuole and the aqueous vacuolar sap.

Experiments from this point of view have been made on Nitella flexilis and Valonia macrophysa. The results are presented here with Valonia, the cells of which consist of an outer cell wall, an inner protoplasmic layer surrounding a relatively large central vacuole filled with sap, at about pH 5.8 and containing about 0.6 M halides.

We may assume 3 that the dye diffuses through the protoplasm into the vacuole in succession through an outer non-aqueous layer, a middle aqueous layer, an inner non-aqueous layer (surrounding the vacuole), and then into the vacuolar sap.

By applying these ideas experimentally we can predict the behavior of the dyes in penetrating Valonia. The dye in sea water at pH 9.5 or at pH 5.5 is shaken with chloroform so as to represent the two non-aqueous layers. Then the chloroform is removed and shaken with freshly collected Valonia sap.