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 uptake of cobalt occurs via selective, inhibitable, calcium uptake routes. Modulation of the calcium transport system was performed using general calcium channel blockers (Cd2+, La3+, Mg2+), a voltage-dependent calcium channel blocker (diltiazem) and an intraperitoneal CaCl2 injection. 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 the gills. Diltiazem displayed only an inconsistent, concentration-independent blocking of the uptake of both Co2+ and Ca2+. All inhibitors which inhibit Ca2+ uptake also inhibit Co2+ uptake. However, a clear difference in the degree of inhibition of uptake of both elements is observed. Two possible explanations are suggested (1) Co2+ and Ca2+ are both transported through the gills via the same transport system or (2) the calcium transport system is not the only system involved in the transport of Co2+.