Auxiliary subunits operate as a molecular switch in determining gating behaviour of the unitary N‐type Ca2+ channel current in Xenopus oocytes

1 We systematically examined the biophysical properties of ω‐conotoxin GVIA‐sensitive neuronal N‐type channels composed of various combinations of the α1B, α2/δ and β1b subunits in Xenopus oocytes. 2 Whole‐cell recordings demonstrated that coexpression of the β1b subunit decelerated inactivation, whereas the α2/δ accelerated both activation and inactivation, and cancelled the kinetic effects of the β1b. The α2/δ and the β1b controlled voltage dependence of activation differently: the β1b significantly shifted the current‐voltage relationship towards the hyperpolarizing direction; however, the α2/δ shifted the relationship only slightly in the depolarizing direction. The extent of voltage‐dependent inactivation was modified solely by the β1b. 3 Unitary currents measured using a cell‐attached patch showed stable patterns of opening that were markedly different among subunit combinations in their kinetic parameters. The α2/δ and the β1b subunits also acted antagonistically in regulating gating patterns of unitary N‐type channels. Open time was shortened by the α2/δ, while the fraction of long opening was enhanced by the β1b. The α2/δ decreased opening probability (Po), while the β1b increased Po. α1Bα2/δβ1b produced unitary activity with an open time distribution value in between those of α1Bα2/δ and α1Bβ1b. However, both the α2/δ and the β1b subunits reduced the number of null traces. 4 These results suggest that the auxiliary subunits alone and in combination contribute differently in forming gating apparatuses in the N‐type channel, raising the possibility that subunit interaction contributes to the generation of functional diversity of N‐type channels in native neuronal preparations also.