ALPHA(5) SUBUNIT FORMS FUNCTIONAL ALPHA(3)BETA(4)ALPHA(5) NACHRS IN TRANSFECTED HUMAN-CELLS

NACHRS heterologously expressed in human cells after transient transfe ction with alpha(3) beta(4) alpha(5) or alpha(3) beta(4) subunit cDNAs exhibited similar sensitivities to antagonists and comparable functio nal channel profiles. However, the sum of two Hill equations was requi red for best fitting the ACh dose-current response curves after co-exp ression of alpha(5), alpha(3) and beta(4) subunits. One component was comparable to that obtained in alpha(3) beta(4)-transfected cells, whi le the additional component, putatively attributed to an alpha(3) beta (4) alpha(5) nAChR population, showed a Hill coefficient >2 and a nine -fold greater half-maximal ACh concentration (EC50). These results sug gest that the alpha(5) subunit participates in the assembly of alpha(3 ) beta(4) alpha(5) nAChRs complexes in human cells, adding a new membe r to the family of neuronal nicotinic receptors.