The electrical potential difference across the epithelium of isolated gills of the crayfish Austropotamobius pallipes (Lereboullet).

There has been a considerable amount of work on the electrical potential differences and active transport processes of ions across various vertebrate epithelia (Ussing, i960). Little work of this type has been attempted on invertebrate material. As the crustacean gill epithelium has only a single layer of cells separating the body fluid and the external medium, it should be particularly suitable for such studies. Crustacea living in hypo-osmotic media take up NaCl from the medium and it has been assumed that this uptake is across the gill epithelium. In the case of Eriocheir it has been shown that isolated gills can take up NaCl rapidly from a dilute NaCl solution (Koch, 1954). There have been measurements of the electrical potential difference between the haemolymph and dilute outer medium in whole Austropotamobius. The values range from —4-1 to — 6-6 mV. in tap water (Bryan, i960) and — 5 to — 47 mV. in a medium of 0-3 mM/1. KC1 (Shaw, i960). The sign of the potential is that of the haemolymph with respect to the medium. These results indicate that both chloride and sodium must be actively transported into the haemolymph against an electrochemical potential difference. In this paper measurements of the electrical potential difference across the epithelium of isolated perfused gills of Austropotamobius pallipes are reported.