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Effect of MK-801 at the human alpha 7 nicotinic acetylcholine receptor
1Neuroscience Research, Abbott Laboratories, Abbott Park, IL 60064, USA.
Abstract:
Responses of the human alpha 7 nicotinic acetylcholine receptor (alpha 7 nAChR) expressed in Xenopus laevis oocytes were quantified in the presence of barium (10 mM) to prevent secondary activation of Ca(2+)-dependent Cl- currents and atropine (2 microM) to block endogenous muscarinic receptors. Acetylcholine (ACh) elicited responses with EC50 values of 177 +/- 32 microM to 272 +/- 26 microM in different experiments. Responses to ACh (200 microM) were blocked by the nAChR antagonists alpha-bungarotoxin (IC50 = 0.54 +/- 0.04 nM), methyllycaconitine (IC50 = 0.64 +/- 0.08 nM) and mecamylamine (IC50 = 1.8 +/- 02 microM). Additionally, MK-801, a non-competitive blocker of N-methyl-D-aspartate (NMDA) sensitive glutamate receptor channels, inhibited the human alpha 7 nAChR. This effect was not stereoselective; the IC50 for (+)-MK-801 was 15 +/- 3 microM while that for (-)-MK-801 was 14 +/- 3 microM. The inhibition by MK-801, in contrast to methyllycaconitine, was dependent upon cell potential, consistent with a mechanism involving channel blockade. The inhibition by MK-801 reversed slowly (time constant approximately 20 min) compared to that by methyllycaconitine (100% recovery within 10 min). However, MK-801 did not appear to be trapped in the channel because the recovery from inhibition showed little dependence upon stimulation rate or cell potential. Thus, MK-801 acted as a non-stereoselective alpha 7 nAChR inhibitor that was only about 8-fold less potent than the nAChR antagonist mecamylamine and probably acted through channel blockade.
Insights
The human alpha 7 nicotinic acetylcholine receptor (alpha 7 nAChR) is inhibited by MK-801, a glutamate receptor antagonist. MK-801 acts as a non-competitive channel blocker for alpha 7 nAChR, similar to mecamylamine.
Area of Science:
- Neuroscience
- Pharmacology
- Molecular Biology
Background:
- The human alpha 7 nicotinic acetylcholine receptor (alpha 7 nAChR) is a key target in neuroscience.
- Understanding its modulation is crucial for developing therapeutic agents.
Purpose of the Study:
- To quantify the responses of human alpha 7 nAChR expressed in Xenopus laevis oocytes.
- To investigate the inhibitory effects of MK-801 on alpha 7 nAChR function.
Main Methods:
- Electrophysiological recordings in Xenopus laevis oocytes expressing human alpha 7 nAChR.
- Application of acetylcholine (ACh) to elicit responses.
- Inhibition studies using known alpha 7 nAChR antagonists (alpha-bungarotoxin, methyllycaconitine, mecamylamine) and MK-801.
- Analysis of dose-response relationships and kinetic properties of inhibition.
Main Results:
- Acetylcholine (ACh) elicited concentration-dependent responses with EC50 values ranging from 177 to 272 microM.
- Specific nAChR antagonists potently blocked ACh-induced responses.
- MK-801 non-competitively inhibited alpha 7 nAChR in a non-stereoselective manner (IC50 for enantiomers around 14-15 microM).
- MK-801 inhibition was voltage-dependent and reversed slowly, consistent with channel blockade.
Conclusions:
- MK-801 acts as a non-stereoselective, non-competitive inhibitor of the human alpha 7 nAChR.
- The mechanism of MK-801 inhibition involves channel blockade, distinct from competitive antagonists.
- MK-801 demonstrates significant potency against alpha 7 nAChR, comparable to some nAChR-specific antagonists.