The neuronal nicotinic acetylcholine receptor subunits alpha 2, alpha 3, and alpha 4 form functional receptors with the beta 2 subunit. Each of these subunit combinations shows two distinct open states (referred to as primary and secondary). The primary open states of alpha 2 beta 2, alpha 3 beta 2, and alpha 4 beta 2 receptors were 33.6 +/- 1.8 pS, 15.4 +/- 0.8 pS, and 13.3 +/- 1.5 pS, respectively. The open times of the alpha 3 beta 2 primary open state were significantly longer than the open times of the other primary conductance states. The secondary open states of alpha 2 beta 2 and alpha 3 beta 2 were 15.5 +/- 1.3 pS and 5.1 +/- 0.4 pS, respectively. Secondary open states were seen infrequently with alpha 4 beta 2. Oocytes injected with alpha 2 RNA and a 9-fold excess of beta 2 RNA showed an enhanced expression of the secondary open state.