Effect of MK-801 at the human α7 nicotinic acetylcholine receptor

Abstract

Responses of the human α7 nicotinic acetylcholine receptor (α7 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 μM) to block endogenous muscarinic receptors. Acetylcholine (ACh) elicited responses with EC 50 values of 177 ± 32 μM to 272 ± 26 μM in different experiments. Responses to ACh (200 μM) were blocked by the nAChR antagonists α-bungarotoxin (IC 50 = 0.54 ± 0.04 nM), methyllycaconitine (IC 50 = 0.64 ± 0.08 nM) and mecamylamine (IC 50 = 1.8 ± 02 μM). Additionally, MK-801, a non-competitive blocker of N-methyl- d-aspartate (NMDA) sensitive glutamate receptor channels, inhibited the human α7 nAChR. This effect was not stereoselective; the IC 50 for (+)-MK-801 was 15 ± 3 μM while that for (−)-MK-801 was 14 ± 3 μM. 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 α7 nAChR inhibitor that was only about 8-fold less potent than the nAChR antagonist mecamylamine and probably acted through channel blockade.