The gadolinium ion: A potent blocker of calcium channels and catecholamine release from cultured chromaffin cells

Abstract

Gadolinium (Gd 3+) is a trivalent ion of the lanthanide series which has a high charge density and a similar ionic radius to Ca 2+. The effects of gadolinium ions on [ 3H]noradrenaline output and 45Ca fluxes during resting conditions and stimulation were investigated in cultured bovine chromaffin cells. Chromaffin cells isolated from bovine adrenal medullae were plated on collagen-coated dishes (10 6 cells/dish) in a medium containing 10% fetal calf serum. Seven-day-old cells were used in all studies. Exposure of chromaffin cells to 0.05mM Gd 3+ produced 80 ± 5% and 81 ± 4% inhibition of the secretory responses to 10 −4M acetylcholine and 56 mM K + respectively. Doubling of the extracellular concentration of Gd 3+ produced an 87 ± 3% and 100 ± 2% inhibition of the acetylcholine-induced and K +-induced release of [ 3H]noradrenaline. Gd 3+ (0.05 mM) also produced a parallel shift to the right in the dose-response relationship between extracellular Ca 2+ concentrations and [ 3H]noradrenaline output during acetylcholine stimulation. This observation suggests a competitive antagonism between Ca 2+ and Gd 3+ in stimulus-secretion coupling. Gd 3+ (0.05 mM) was an effective inhibitor (92.3 ± 0.7%) of the uptake of 45Ca into chromaffin cells induced by a depolarizing concentration (56 mM) of K +. Furthermore, Gd 3+ also inhibited the increase in both Ca 2+ − Ca 2+ exchange mechanism and [ 3H]noradrenaline output observed in chromaffin cells upon the reintroduction of Ca 2+ into a Ca 2+]-free incubation medium. The results, which were obtained using low concentrations of Gd 3+, indicate that gadolinium is a powerful inhibitor of the Ca 2+ movements which are required for triggering amine release from chromaffin cells by different secretagogues. Moreover, the results also suggest that Gd 3+ might be a useful tool for release and electrophysiological studies in other Ca 2+-dependent systems.