Ca v 2.1 channels divide into two populations at resting membrane potentials.

Voltage-gated CaV2.1 channels mediate P/Q-type currents and are the predominant CaV isoform in the brain, linking neuronal excitability to neurotransmitter release. Their pore-forming α1A subunit has four homologous, non-identical, voltage-sensing domains (VSDs) but their contributions to voltage-dependent regulation remain unclear. We utilized cut-open oocyte voltage-clamp fluorometry to optically track the activation of individual VSDs in conducting CaV2.1 complexes composed of the human α1A, together with α2δ and β2a, in the absence of Ca2+-dependent regulation. Previously, we showed that VSDs III and IV activate with a single Boltzmann distribution and have similar midpoint potentials (V0.5,III≈V0.5,IV≈−65mV).