Neurotoxicity of channel mutations in heterologously expressed alpha 7-nicotinic acetylcholine receptors

Nicotinic acetylcholine receptors (nAChR) composed of chick alpha7 subunits mutated to threonine at amino acid valine-251 in the putative channel-lini ng M2 domain were expressed heterologously in several neuron-like and non-n euronal mammalian cell lines. Expression of mutant alpha7-nAChR is toxic to neuron-like cells of the human neuroblastoma cell lines SH-SY5Y and IMR-32 , but not to several other cell types. Growth in the presence of the alpha7 -nAChR antagonist methyllycaconitine (MLA) protects against neurotoxicity, as does gradual downregulation of functional, mutant alpha7-nAChR in surviv ing transfected SH-SY5Y cells. Relative to wild-type alpha7-nAChR, function al alpha7-nAChR mutants show a higher affinity for agonists, slower rates o f desensitization, and sensitivity to dihydro-beta -erythroidine (DH betaE) as an agonist, but they retain sensitivity to MLA as a competitive antagon ist. These findings demonstrate that expression of hyperfunctional, mutant forms of Ca2+-permeable alpha7-nAChR is toxic to neuron-like cells.