Auxiliary subunits operate as a molecular switch in determining gating behaviour of the unitary N‐type Ca 2+ 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 α 1B , α 2 /δ and β 1b subunits in Xenopus oocytes. 2 Whole‐cell recordings demonstrated that coexpression of the β 1b subunit decelerated inactivation, whereas the α 2 /δ accelerated both activation and inactivation, and cancelled the kinetic effects of the β 1b . The α 2 /δ and the β 1b controlled voltage dependence of activation differently: the β 1b significantly shifted the current‐voltage relationship towards the hyperpolarizing direction; however, the α 2 /δ shifted the relationship only slightly in the depolarizing direction. The extent of voltage‐dependent inactivation was modified solely by the β 1b . 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 α 2 /δ and the β 1b subunits also acted antagonistically in regulating gating patterns of unitary N‐type channels. Open time was shortened by the α 2 /δ, while the fraction of long opening was enhanced by the β 1b . The α 2 /δ decreased opening probability ( P o ), while the β 1b increased P o . α 1B α 2 /δβ 1b produced unitary activity with an open time distribution value in between those of α 1B α 2 /δ and α 1B β 1b . However, both the α 2 /δ and the β 1b 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.