The "calcium antagonist" TMB-8 [3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester] is a potent, non-competitive, functional antagonist at diverse nicotinic acetylcholine receptor subtypes.
[3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester] (TMB-8) has seen wide use as an "intracellular Ca2+ antagonist." However, this study shows that TMB-8 acts as a noncompetitive, functional antagonist at diverse nicotinic acetylcholine receptor (nAChR) subtypes with potencies that exceed those for other reported effects of TMB-8, including inhibition of intracellular Ca2+ mobilization. TMB-8 is a potent inhibitor (IC50 approximately 400 nM) of agonist-stimulated ion flux mediated by functional human muscle nAChR or ganglionic alpha 3 beta 4-nAChR subtypes expressed by TE671/RD or SH-SY5Y cells. TMB-8 is also a potent inhibitor (IC50 approximately 500 nM) of a functional, central nervous system nAChR subtype that mediates nicotinic agonist-stimulated [3H]dopamine release from rat brain synaptosomes. TMB-8 is much less potent (IC50 approximately 30-200 microM) as an inhibitor of high-affinity 3H-labeled acetylcholine or 125I-labeled alpha-bungarotoxin binding to human muscle nAChR, ganglionic alpha 3 beta 4-nAChR, or ganglionic alpha 7-nAChR subtypes. Moreover, functional inhibition by TMB-8 of muscle-type nAChR is due to a reduction in agonist efficacy, but not potency, and is proportionately stronger with increasing agonist concentration, thereby suggesting that TMB-8 acts as a noncompetitive inhibitor. Similar effects are observed for local anesthetics such as tetracaine and procaine (functional IC50 values of approximately 5 and approximately 50 microM, respectively), although TMB-8 is the most potent of these agents. Studies with TMB-8 or BAPTA [1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid] analogues indicate that the amino group of TMB-8 is essential and that Ca2+ chelation is not required for inhibition of nAChR function.(ABSTRACT TRUNCATED AT 250 WORDS)
Division of Neurobiology, Barrow Neurological Institute, Phoenix, Arizona, USA.
M
M
Bencherif
C M
CM
Eisenhour
R J
RJ
Prince
P M
PM
Lippiello
R J
RJ
Lukas
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000378:metabolism / Q000494:pharmacology*; D002999:Clone Cells; D005260:Female; D005707:Gallic Acid / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D018733:Nicotinic Antagonists / Q000378:metabolism / Q000494:pharmacology*; D016716:PC12 Cells; D011869:Radioligand Assay; D051381:Rats; D017207:Rats, Sprague-Dawley; D015222:Sodium Channels / Q000187:drug effects
D002121:Calcium Channel Blockers; D018733:Nicotinic Antagonists; D015222:Sodium Channels; C006014:8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate; D005707:Gallic Acid; D002118:Calcium