Electrical parameters of the cuticle of the posterior gill lamella of the shore crab Carcinus maenas, were measured. When the cuticle was perfused with crab saline (CS) inside and sea water (SW) outside, ionic replacements or dilutions of the bathing solutions produced changes in potential that showed a selective permeability to cations with respect to anions. Similar measurements made with the cuticle bathed in single salt solutions gave the following permeability sequence: NH4+> Rb+> Cs+> K+> Na+≊Ca2+ > Li+> Tris+> Mg2+ HCO3> CH3COO> Cl> SO42-.

From conductance measurements, the permeability of the cuticle to Ca2+ and Na+ was about 10−3cms−1. K+ and NH4+ were about five times more permeant, while Mg2+permeability was 5×10−5 cms−1. The permeability of the cuticle to anions lay between 10−6 and 10−5 cms−1. In addition, the cuticle showed an asymmetrical behaviour. These results suggest that the low anionic cuticular permeability can interfere with ionic exchanges across the whole gill.

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Present address: Laboratoire d'Etude des Régulations Physiologiques, associé à l'Université Louis Pasteur, Centre National de la Recherche Scientifique, 23 rue Becquerel, 67087 Strasbourg, France.

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