The Electrical Potential Difference Across the Epithelium of Isolated Gills of the Crayfish Austropotamobius Pallipes (Lereboullet)

Abstract

A technique is described for recording the electrical potential differences across the epithelium (epithelial potential) of isolated podobranch gills of Austropotamobius pallipes continuously perfused with Ringer solution in various external media. In a medium of 0·01 Ringer, in which the animals had previously been kept, the mean epithelial potential ± standard deviation was —60 ±12 mV. (Sign defines potential of body fluid with respect to external medium.) Chloride, sodium and potassium must be actively transported into the body fluid against an electrochemical gradient. Calcium and magnesium ions appear to be approximately in equilibrium. The steady-state membrane potentials were recorded in various external concentrations of Ringer solution. The potential is about zero with Ringer solution outside and rises to a maximum with 0·01 Ringer outside. Changes of the electrical potential were recorded when the concentration of a single electrogenic ion was changed in the external medium (0·01 Ringer), and were used to define an apparent transport number of the ion in the outer cell membrane. There was no correlation between the transport numbers and the epithelial potential. There was a continuous gradation of gill types from a predominantly cation-permeable type towards a more chloride permeable type. There is a correlation between the type of gill and the position in the gill series. The properties of the epithelial cells of Austropotamobius gill are significantly different from those of the epithelial cells of frog skin. It is suggested that in Austropotamobius a chloride pump is situated in the outer cell membrane.