ABT-200, a norepinephrine uptake inhibitor, blocks Ca 2+ signals in chromaffin cells

Abstract

We previously described inhibition by racemic (±)-(1′R ∗,3R ∗)-3- phenyl-1-[1′,2′,3′,4′- tetrahydro-5′,6′- methyl enedioxy-1′- napthalenyl-methyl]-pyrrolidine methanesulfonate (ABT-200), and its two constituent enantiomers, SS,ABT-200 and RR,ABT-200, of nicotine-stimulated but not histamine-stimulated catecholamine release from bovine adrenal chromaffin cells. To test the hypothesis that this inhibition reflects a blockade of Ca 2+ influx, we used fura-2 loaded chromaffin cells to investigate cytosolic Ca 2+ signals. We found that SS,ABT-200 inhibited nicotine- and K +-stimulated Ca 2+ signals, both of which depend on Ca 2+ influx. However, the early phase of the histamine-stimulated Ca 2+ signals, which depends on Ca 2+ mobilization from intracellular stores, was unaffected. We also examined ion flux through the nicotinic receptor by measuring 86rubidium + ( 86Rb +) efflux from preloaded mouse midbrain synaptosomes. We found that SS,ABT-200 partially inhibited nicotine-stimulated 86Rb + efflux, suggesting that it blocks ion flux through the nicotinic receptor directly. These data support a model in which ABT-200 blocks nicotine-stimulated catecholamine release by inhibiting cation flux through multiple channels.