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 muA cm-2 and a resistance (R(t)) of 25 +/- 3 OMEGA 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 oua-bain (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 an increase of both inward negative I(sc) and R(t). The dose dependence of the diuretic showed a maximal effect between 50 and 200 mumol l-1 with a half-maximal blocker concentration (K(AMI)) of ca. 10 mumol 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-.