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⁺.