Abstract
Inhibition of neuronal nicotinic receptors can be regulated by sequence in the β subunit second transmembrane domain (TM2). The incorporation of a β4(6′F10′T) subunit, which contains sequence from the muscle β subunit at the TM2 6′ and 10′ positions of the neuronal β4 subunit, increases the loss of receptor responsiveness after the application of acetylcholine (ACh), nicotine, or 3-(2,4-dimethoxybenzylidene)-anabaseine (DMXB), an α7-selective partial agonist. Inhibition of receptor responsiveness following agonist exposure may occur through either an enhancement of desensitization, increased channel block by an agonist, or alternatively via allosteric modulation. Although DMXB produces very little activation of either α3β4 or α3β4(6′F10′T) receptors, DMXB shows an enhanced use-and voltage-dependent inhibition of α3β4(6′F10′T) receptors compared with wild-type. In contrast, the α4β2-selective agonist (E)-N-methyl-4-(3-pyridinyl)-3-butene-1-amine (TC-2403, previously identified as RJR-2403) shows increased activation of α3β4(6′F10′T) receptors compared with α3β4 receptors (as related to ACh activation) but with no significant increase in antagonist activity. The interaction between the binding of local anesthetics and the functional inhibition produced by these agonists was evaluated. The binding of the local anesthetics to their inhibitory sites does not affect inhibitory effects of DMXB and nicotine. However, TC-2403 can protect receptor function from the inhibitory effects of other agonists, suggesting that TC-2403, as well as agonists that cause inhibition, may be binding to an allosteric site, either promoting or inhibiting channel opening. The ability of TC-2403 to protect receptor function from agonist-induced inhibition may point toward valuable new combination drug therapies.
Footnotes
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Studies were supported by the University of Florida College of Medicine Incentive award and by National Institutes of Health Grant NS32888-02.
- Abbreviations:
- ACh
- acetylcholine
- AChR
- ACh receptor
- TM2
- second transmembrane domain
- TC-2403
- (E)-N-methyl-4-(3-pyridinyl)-3-butene-1-amine
- DMXB
- 3-(2,4-dimethoxybenzylidene)-anabaseine
- QX-314
- 2-(triethylamino)-N-(2,6-dimethylphenyl)-acetamide
- tetracaine
- N,N-dimethylaminoethyl-4-butylaminobenzoate
- Received October 16, 2001.
- Accepted November 26, 2001.
- The American Society for Pharmacology and Experimental Therapeutics
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