Ca_V2.1 α₁ subunit motifs that control presynaptic Ca_V2.1 subtype abundance are distinct from Ca_V2.1 preference

Abstract

Presynaptic voltage‐gated Ca²⁺ channel (Ca_V) subtype abundance at mammalian synapses regulates synaptic transmission in health and disease. In the mammalian central nervous system (CNS), most presynaptic terminals are Ca_V2.1 dominant with a developmental reduction in Ca_V2.2 and Ca_V2.3 levels, and Ca_V2 subtype levels are altered in various diseases. However, the molecular mechanisms controlling presynaptic Ca_V2 subtype levels are largely unsolved. Because the Ca_V2 α₁ subunit cytoplasmic regions contain varying levels of sequence conservation, these regions are proposed to control presynaptic Ca_V2 subtype preference and abundance. To investigate the potential role of these regions, we expressed chimeric Ca_V2.1 α₁ subunits containing swapped motifs with the Ca_V2.2 and Ca_V2.3 α₁ subunit on a Ca_V2.1/Ca_V2.2 null background at the calyx of Held presynaptic terminals. We found that expression of Ca_V2.1 α₁ subunit chimeras containing the Ca_V2.3 loop II–III region or cytoplasmic C‐terminus (CT) resulted in a large reduction of presynaptic Ca²⁺ currents compared to the Ca_V2.1 α₁ subunit. However, the Ca²⁺ current sensitivity to the Ca_V2.1 blocker agatoxin‐IVA was the same between the chimeras and the Ca_V2.1 α₁ subunit. Additionally, we found no reduction in presynaptic Ca²⁺ currents with Ca_V2.1/2.2 cytoplasmic CT chimeras. We conclude that the motifs in the Ca_V2.1 loop II–III and CT do not individually regulate Ca_V2.1 preference, although these motifs control Ca_V2.1 levels and the Ca_V2.3 CT contains motifs that negatively regulate presynaptic Ca_V2.3 levels. We propose that the motifs controlling presynaptic Ca_V2.1 preference are distinct from those regulating Ca_V2.1 levels and may act synergistically to impact pathways regulating Ca_V2.1 preference and abundance. image