Branchial cobalt uptake in the carp, Cyprinus carpio: Effect of calcium channelblockers and calcium injection

Using tracer-uptake studies we investigated whether the branchial uptakeof cobalt occurs via selective, inhibitable, calcium uptake routes.Modulation of the calcium transport system was performed using generalcalcium channel blockers (Cd2+, La3+,Mg2+), a voltage-dependent calcium channel blocker (diltiazem)and an intraperitoneal CaCl2 injection. Adding Cd2+ orMg2+ to thewater or injecting the fish with theCa2+-solution resulted in decreased Co2+ andCa2+ uptake rates. Addition of La3+ reducedCa2+ and Co2+ uptake rates except forCo2+ uptake in the gills. Diltiazem displayed only aninconsistent, concentration-independent blocking of the uptake of bothCo2+ and Ca2+. All inhibitors which inhibitCa2+ uptake also inhibit Co2+ uptake. However, aclear difference in the degree of inhibition of uptake of both elements isobserved. Two possible explanations are suggested (1) Co2+ andCa2+ are both transported through the gills via the sametransport system or (2) the calcium transport system is not the only systeminvolved in the transport of Co2+.