Ionic permeabilities of the gill lamina cuticle of the crayfish, Astacus leptodactylus (E).

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Abstract
The cuticle of the gill lamina of the crayfish A. leptodactylus (E), mechanically isolated, was mounted in an Ussing chamber and examined for its electrical properties. The cuticle of the gill lamina obtained from exuviae had similar properties. When perfused with artificial fresh water (AFW) outside and Van Harreveld solution (VH) inside, the transcuticular potential Voi was negative with respect to the inside, and close to the equilibrium potential for Cl- (ECl-). CH3COO-, HCO3-, SO42- and cations (Na+, K+, Ca2+, Mg2+ and NH4+) behaved as impermeant ions with respect to Cl-. A decrease of pH (brought about with CO2) from 8.5 to 6.0 in AFW, VH or both had no effect on the potential. The cuticle area specific conductance was 20-30 mS/cm2 when superinfused with AFW outside and VH inside. The conductance decreased linearly with log [Cl-] when Cl- was replaced by CH3COO-. Rectification was obvious when internal Cl- was reduced to 5 mmol/l. The Cl- selectively of the cuticle could also be demonstrated in perfusing the cuticle with a single salt (NaCl, KCl, CaCl2, MgCl2 or LaCl3) and in diluting that salt on one side of the preparation or in replacing Cl- by CH3COO-, SO42- and HCO3-. The potential changed almost linearly with log [Cl-] and was close to ECl-. The inner face of the cuticle was found to be slightly less selective than the outer face. The relative permeabilities were calculated to be: PCl- = 1, PNa+ = 0.001, PHCO3- = 0.0006, PCH3COO- = 0.0002. The dilution of a Cl--free salt resulted in a catonic potential. The relative permeabilities of cations (NH4+, K+, Na+, Ca2+ and MG2+) were found to range within a factor 2. The permeability of the cuticle to HCO3-, CH3COO- and SO42- was 2-5 times lower. The cuticle conductance was linearly related to the activity of the salt perfusing the 2 sides of the preparation at equal concentrations. The molar area specific conductance to chloride salts was 14 (mS/cm2)/(mmol/l). That of Cl--free salts ranged from 1 to 20 (.mu.S/cm2)/(mmol/l) depending on the salt used. It was deduced that PCl- is 2 .times. 10-3 cm/s and that all the other ions tested have permeabilities of 10-7-10-6 cm/s. With large intensity current pulses the cuticle exhibited rectifying properties and an asymmetrical behavior. Increasing the pH of the perfusing solution reduced the transcuticular potential established with a Cl- gradient. In Cl-free media and at high pH, large potentials were obtained with a pH gradient. The conductance of the cuticle increased with pH and a permeability to OH- of about 10-3 cm/s was computed. The soft thorax and abdomen cuticle of the crayfish had no selective properties and its conductance was low. The soft cuticle of the gill lamina of the lobster had no selective properties but its conductance was high. Results show a high selectivity of the gill lamina cuticle to Cl- and OH- over other ions normally present in the hemolymph and in the fresh water. This selectivity is likely to be located in the epicuticular layer and is specific to the gill lamina of the crayfish. The cuticle could favor Cl--OH- exchange and Na+-Cl- co-transport through the gills.