Chromaffin cell catecholamine secretion: bisindolylmaleimide compounds exhibit novel and potent antagonist effects at the nicotinic cholinergic receptor in pheochromocytoma cells.
Activation of protein kinase C (PKC) stimulates nicotine-induced catecholamine secretion. PKC down-regulation by prolonged pretreatment with phorbol 12-myristate 13-acetate diminished nicotine-induced catecholamine secretion only slightly (approximately 16%), suggesting substantial PKC independence of nicotinic receptor activation. However, we found that bisindolylmaleimide compounds (which are also putative PKC chemical inhibitors) dramatically inhibited nicotine-induced catecholamine secretion (IC(50) values of approximately 24-37 nM). This inhibition was specific for the nicotinic cholinergic receptor. Catecholamine secretion induced by other nicotinic agonists (such as epibatidine, anatoxin, or cytisine) was also powerfully antagonized by bisindolylmaleimide II (IC(50) values of approximately 60-90 nM). Even high-dose nicotinic agonists failed to overcome the inhibition by bisindolylmaleimide II, suggesting noncompetitive nicotinic antagonism by this class of compounds. Nicotinic inhibition by bisindolylmaleimide seemed not to be readily reversible. Structure-activity studies of bisindolylmaleimide compounds revealed that bisindolylmaleimides I through III are the most potent nicotinic antagonists at the nicotinic cholinergic receptor in PC-12 cells (IC(50) < or =37 nM), whereas bisindolylmaleimide IV and V have far less nicotinic antagonist activity (IC(50) >1 microM); the active compounds I through III have cationic tails at an indole nitrogen, whereas the least potent compounds IV and V do not. By contrast, a free NH within the maleimide ring is crucial for PKC inhibition by this class of compounds. We conclude that bisindolylmaleimides I through III are some of the most potent noncompetitive neuronal nicotinic antagonists, indeed the most potent such antagonists we have observed in PC-12 cells. Nicotinic antagonism of these compounds seems to be independent of PKC inhibition.
Mahata
Manjula
M
Department of Medicine and Center for Molecular Genetics, University of California, San Diego, La Jolla, California 92093-0838, USA.
Mahapatra
Nitish R
NR
O'Connor
Daniel T
DT
Mahata
Sushil K
SK
D000818:Animals; D001667:Binding, Competitive; D002395:Catecholamines / Q000378:metabolism*; D019439:Chromaffin Cells / Q000187:drug effects* / Q000378:metabolism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D007211:Indoles / Q000494:pharmacology*; D008301:Maleimides / Q000494:pharmacology*; D009538:Nicotine / Q000378:metabolism; D018733:Nicotinic Antagonists / Q000494:pharmacology; D016716:PC12 Cells; D010673:Pheochromocytoma / Q000378:metabolism / Q000473:pathology*; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D011978:Receptors, Nicotinic / Q000378:metabolism*
D002395:Catecholamines; D004791:Enzyme Inhibitors; D007211:Indoles; D008301:Maleimides; D018733:Nicotinic Antagonists; D011978:Receptors, Nicotinic; C116174:bisindolylmaleimide II; D009538:Nicotine; D011493:Protein Kinase C; C088060:bisindolylmaleimide