ABT-200, a norepinephrine uptake inhibitor, blocks Ca2+ signals in chromaffin cells.
We previously described inhibition by racemic (+/-)-(1'R*,3R*)-3-phenyl-1- [1',2',3',4'-tetrahydro-5',6'-methylenedioxy-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 Ca2+ influx, we used fura-2 loaded chromaffin cells to investigate cytosolic Ca2+ signals. We found that SS,ABT-200 inhibited nicotine- and K(+)-stimulated Ca2+ signals, both of which depend on Ca2+ influx. However, the early phase of the histamine-stimulated Ca2+ signals, which depends on Ca2+ 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.
Department of Pharmacology, University of Colorado Health Sciences Center, Denver 80262.
J A
JA
Firestone
M J
MJ
Marks
G A
GA
Gerhardt
M D
MD
Browning
D000311:Adrenal Glands / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002417:Cattle; D016257:Fura-2; D006632:Histamine / Q000494:pharmacology; D066298:In Vitro Techniques; D008636:Mesencephalon / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D014179:Neurotransmitter Uptake Inhibitors / Q000494:pharmacology*; D009538:Nicotine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism*; D011188:Potassium / Q000037:antagonists & inhibitors / Q000494:pharmacology; D011978:Receptors, Nicotinic / Q000187:drug effects; D012414:Rubidium Radioisotopes; D013237:Stereoisomerism; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism; D013788:Thalamus / Q000187:drug effects / Q000378:metabolism
D002121:Calcium Channel Blockers; D014179:Neurotransmitter Uptake Inhibitors; D011978:Receptors, Nicotinic; D012414:Rubidium Radioisotopes; D009538:Nicotine; D006632:Histamine; D011188:Potassium; D016257:Fura-2; D009638:Norepinephrine