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

Abstract

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 (Isc) of-240±65 μAcm-2 and a resistance (Rt) of 25±3 Ωcm2 (n=8). Substitution of Cl- (gluconate) on both sides of the preparation resulted in a decrease of Isc by more than 90% at constant Rt. Isc disappeared and Rt increased after substitution of Na+ (choline). When ouabain (2 mmol l-1) was applied to the internal NaCl-saline, Isc decreased and Rt remained unchanged. Internal addition of 0.1 mmol l-1 acetazolamide left Isc and Rt unaffected. Application of amiloride to the external NaCl saline resulted in a increase of both inward negative Isc and Rt. The dose dependence of the diuretic showed a maximal effect between 50 and 200 μmol l-1 with a half-maximal blocker concentration (KAMI) of ca. 10 μmol 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-.