BRANCHIAL COBALT UPTAKE IN THE CARP, CYPRINUS-CARPIO - EFFECT OF CALCIUM-CHANNEL BLOCKERS AND CALCIUM INJECTION

Using tracer-uptake studies we investigated whether the branchial upta ke of cobalt occurs via selective, inhibitable, calcium uptake routes. Modulation of the calcium transport system was performed using genera l calcium channel blockers (Cd2+, La3+, Mg2+), a voltage-dependent cal cium channel blocker (diltiazem) and an intraperitoneal CaCl2 injectio n. Adding Cd2+ or Mg2+ to the water or injecting the fish with the Ca2 +-solution resulted in decreased Co2+ and Ca2+ uptake rates. Addition of La3+ reduced Ca2+ and Co2+ uptake rates except for Co2+ uptake in t he gills. Diltiazem displayed only an inconsistent, concentration-inde pendent blocking of the uptake of both Co2+ and Ca2+. All inhibitors w hich inhibit Ca2+ uptake also inhibit Co2+ uptake. However, a clear di fference in the degree of inhibition of uptake of both elements is obs erved. Two possible explanations are suggested (1) Co2+ and Ca2+ are b oth transported through the gills via the same transport system or (2) the calcium transport system is not the only system involved in the t ransport of Co2+.