INFLUENCE OF PH ON SKIN PERMEATION OF AMINO-ACIDS

Skin permeation of amino acids through excised rat skin was measured a t various pH values. The permeabilities varied with the donor pH and a mino acid, indicating that each ionic species of amino acid may have a different permeability. The permeability coefficient of each ion was estimated from the permeability-pH profiles using the dissociation con stants. The estimated values for mono-cation and uncharged zwitterion were not dependent on the lipophilicity but on the size of the amino a cid, suggesting a porous mechanism of transport. The permeability coef ficient was highest for di-cation, followed by mono-cation, positively charged, uncharged and negatively charged zwitterions. The electrical potential difference across the skin was too small to affect the perm eation of ions. The permselective property of skin thus seems to be de termined by the difference of diffusivity in aqueous pores of skin due to the hydration of ions and other factors.