Paradoxical allosteric effects of competitive inhibitors on neuronal alpha7 nicotinic receptor mutants.
Mutation of the conserved leucine residue, in the second transmembrane domain of the neuronal alpha7 acetylcholine receptor to a threonine (L247T) causes pleiotropic alterations of receptor properties. In this study we examined the effects of competitive inhibitors on the alpha7-L247T physiological responses. While the alpha7 competitive inhibitor dihydro-beta-erythroidine evoked a current comparable to that induced by ACh, other inhibitors such as methyllycaconitine (MLA) and alpha-bungarotoxin (alpha-Bgt) caused a blockade of alpha7-L247T to ACh activation. When applied in the absence of ACh, MLA or alpha-Bgt reduced the cell leakage current, showing that alpha7-L247T displays a significant fraction (10%) of spontaneously open channels. These data can be interpreted in terms of an allosteric model, assuming that the L247T mutant possesses a low isomerization constant L and that MLA and alpha-Bgt stabilize the closed, resting state.
Bertrand
S
S
Department of Physiology, Medical Faculty, CMU, Geneva, Switzerland.
Devillers-Thiéry
A
A
Palma
E
E
Buisson
B
B
Edelstein
S J
SJ
Corringer
P J
PJ
Changeux
J P
JP
Bertrand
D
D
D000109:Acetylcholine / Q000494:pharmacology*; D000157:Aconitine / Q000031:analogs & derivatives / Q000494:pharmacology; D000494:Allosteric Regulation; D019943:Amino Acid Substitution; D000818:Animals; D001667:Binding, Competitive; D002038:Bungarotoxins / Q000494:pharmacology*; D004079:Dihydro-beta-Erythroidine / Q000494:pharmacology; D005071:Evoked Potentials / Q000187:drug effects; D007930:Leucine; D016297:Mutagenesis, Site-Directed; D009474:Neurons / Q000502:physiology*; D009865:Oocytes / Q000502:physiology; D011978:Receptors, Nicotinic / Q000096:biosynthesis / Q000737:chemistry / Q000502:physiology*; D011994:Recombinant Proteins / Q000096:biosynthesis; D014981:Xenopus; D064569:alpha7 Nicotinic Acetylcholine Receptor
D002038:Bungarotoxins; D011978:Receptors, Nicotinic; D011994:Recombinant Proteins; D064569:alpha7 Nicotinic Acetylcholine Receptor; C054634:methyllycaconitine; D004079:Dihydro-beta-Erythroidine; D007930:Leucine; D000109:Acetylcholine; D000157:Aconitine