Voltage-clamp measurements on single split lamellae of posterior gills of the shore crab Carcinus maenas

Single split lamella preparations of posterior gills of low-salt adapted shore crabs Carcinus maenas (collected from the Kiel Bay, Baltic Sea in 1991) were mounted in a micro Ussing-chamber. With NaCl salines on both sides we found an outside positive potential difference (PD) of 6.6±1.3 mV, a short-circuit current (I_sc) of-240±65 Acm^-2 and a resistance (R_t) of 25±3 cm² (n=8). Substitution of Cl^- (gluconate) on both sides of the preparation resulted in a decrease of I_sc by more than 90% at constant R_t. I_sc disappeared and R_t increased after substitution of Na⁺ (choline). When ouabain (2 mmol l^-1) was applied to the internal NaCl-saline, I_sc decreased and R_t remained unchanged. Internal addition of 0.1 mmol l^-1 acetazolamide left I_sc and R_t unaffected. Application of amiloride to the external NaCl saline resulted in a increase of both inward negative I_sc and R_t. The dose dependence of the diuretic showed a maximal effect between 50 and 200 mol l^-1 with a half-maximal blocker concentration (K_AMI) of ca. 10 mol l^-1. The results show that the split lamella preparation of posterior gills of C. maenas is a low resistance epithelium which is able to effect a massive, electrogenic and coupled absorption of Na⁺ and Cl^-.