Active extrusion of Ca2+ from epiphysial chondrocytes of normal and rachitic chickens.

Chondrocytes isolated from the epiphysial cartilage of chickens were exposed to either the ionophore A23187 or KCN, in the presence of 0.4 mM-extracellular Ca2+. This treatment elicits a prompt release of cell Ca2+, which can be measured as net cation efflux by a highly sensitive Ca2+-selective electrode system. Pre-exposure of chondrocytes to the metabolic inhibitors 2-deoxy-D-glucose or oligomycin causes a parallel decrease in both cell ATP and ionophore-mediated Ca2+ extrusion. Conversely, substitution of extracellular Na+ with choline produces only a very small decrease in the rate of Ca2+ efflux. This indicates that the ionophore A23187 and cyanide induce the mobilization of intracellular Ca2+, which is then extruded from the cell mainly by an ATP-driven pump system. Chondrocytes isolated from the cartilage of rachitic chickens also exhibit the capacity for extruding Ca2+ by the same mechanism, with an efficiency comparable with that of their normal counterpart.