Differential regulation of current kinetics by the β subunits in N-type calcium channel

Abstract

The N-type voltage-gated calcium channel (CaV2.2) regulates synaptic transmission by controlling calcium influx during membrane depolarization. Auxiliary β subunits act as modulators for the gating properties of various calcium channels. However, the differential effects of β2 splice variants on CaV2.2 current kinetics remain unclear. Here, we elucidate how β2a and β2c subunits distinctly modulate CaV2.2 current kinetics. Using whole-cell voltage-clamp in a heterologous system, we analyzed current decay with a double exponential function model (y = Aexp(−x/τA) + Bexp(−x/τB) + y0). During 10-second depolarizing pulses, the current decayed much more slowly in CaV2.2 with β2a compared to CaV2.2 with β2c. Double exponential fitting uncovered β subunit-dependent patterns in amplitude components (A and B) and time constants (τA and τB). CaV2.2 with β2a showed a dominant slow component (A ≈ 0.88, τA ≈ 2 s) and a minor fast component (B ≈ 0.12, τB ≈ 70 ms). In contrast, CaV2.2 with β2c displayed a predominant fast component (A ≈ 0.85, τA ≈ 116 ms) and a minor slow component (B ≈ 0.15, τB ≈ 3 s). We hypothesize that components A and B represent voltage-dependent inactivation and deactivation, respectively, under sustained depolarization. β2a promotes rapid channel deactivation, allowing the current to reach equilibrium between activation and deactivation quickly with slow inactivation. Conversely, β2c induces rapid overall current decay primarily through accelerated inactivation, overshadowing the gradual deactivation process. Our findings demonstrate a significant functional divergence between membrane-anchored (β2a) and cytosolic (β2c) subunits within the β2 family, highlighting the critical role of β subunit localization in fine-tuning channel function. This study will provide novel insights into the molecular basis of calcium signaling in neurons.