Expression and functional properties of a7 acetylcholine nicotinic receptors are modified in the presence of other receptor subunits

Although alpha 7 nicotinic receptors are predominantly homopentamers, previous reports have indicated that alpha 7 and beta 2 subunits are able to form heteromers. We have studied whether other nicotinic receptor subunits can also assemble with alpha 7 subunits and the effect of this potential association. Coexpression of alpha 7 with alpha 2, alpha 3, or beta 4 subunits reduced to about half, surface a-bungarotoxin binding sites and acetylcholine-gated currents. This is probably because of inhibition of membrane trafficking, as the total amount of alpha 7 subunits was similar in all cases and a significant proportion of mature alpha 7 receptors was present inside the cell. Only beta 4 subunits appeared to directly associate with alpha 7 receptors at the membrane and these heteromeric receptors showed some kinetic and pharmacological differences when compared with homomeric alpha 7 receptors. Finally, we emulated the situation of bovine chromaffin cells in Xenopus laevis oocytes by using the same proportion of alpha 3, beta 4, alpha 5, and alpha 7 mRNAs, finding that a-bungarotoxin binding was similarly reduced in spite of increased currents, apparently mediated by alpha 3 beta 4(alpha 5) receptors.