PARADOXICAL ALLOSTERIC EFFECTS OF COMPETITIVE INHIBITORS ON NEURONAL ALPHA-7 NICOTINIC RECEPTOR MUTANTS

MUTATION of the conserved leucine residue, in the second transmembrane domain of the neuronal alpha 7 acetylcholine receptor to a threonine (L247T) causes pleiotropic alterations of receptor properties. In this study we examined the effects of competitive inhibitors on the alpha 7-L247T physiological responses. While the alpha 7 competitive inhibit or dihydro-beta-erythroidine evoked a current comparable to that induc ed by ACh, other inhibitors such as methyllycaconitine (MLA) and alpha -bungarotoxin (alpha-Bgt) caused a blockade of alpha 7-L247T to ACh ac tivation. When applied in the absence of ACh, MLA or alpha-Bgt reduced the cell leakage current, showing that alpha 7-L247T displays a signi ficant fraction (10%) of spontaneously open channels. These data can b e interpreted in terms of an allosteric model, assuming that the L247T mutant possesses a low isomerization constant L and that MLA and alph a-Bgt stabilize the closed, resting state.