Elucidating the molecular mechanisms controlling synaptic strength in mammalian central nervous system
Creators: name: Li, Jianing
Publisher: name: University of Iowa
Year: 2024
Subjects: subject: ion channel
subject: Neurosciences
subject: FOS: Clinical medicine
subject: Biophysics
subject: Electrophysiology

description: Presynaptic voltage gated Ca2+ channels (CaV) subtype abundance at mammalian synapses regulates synaptic transmission in health and disease. In the mammalian central nervous system (CNS), the CaV2 family of voltage-gated Ca2+ channels, CaV2.1, CaV2.2, CaV2.3, are key regulators of synaptic transmission. CaV2.1 is most efficient at triggering action-potential (AP) evoked release because most CNS presynaptic terminals are CaV2.1 dominant with a developmental reduction in CaV2.2 and CaV2.3 levels, and CaV2 subtype levels are altered in various diseases. Moreover, previous studies indicate fast activation kinetics in CaV2.1 compared to CaV2.2 and CaV2.3. However, the molecular mechanisms controlling presynaptic CaV2 subtype levels and regulating synaptic strength are largely unsolved. The majority of voltage-gated calcium channels (VGCC) contain α1, β and α1δ subunits. The α1 subunit is the pore-forming subunit, which determines CaV2 subtype and contains multiple motifs implicated in regulating presynaptic CaV2 levels. Since these cytoplasmic motifs contain varying levels of sequence conservation, they are proposed to control presynaptic CaV2 subtype preference and abundance.
description: To investigate the potential role of these regions, we expressed chimeric CaV2.1 α1 subunits containing swapped motifs with the CaV2.2 and CaV2.3 α1 subunit on a CaV2.1/CaV2.2 null background at the calyx of Held presynaptic terminal, a large CaV2.1 dominant presynaptic terminal, and performed direct presynaptic calcium current recordings to determine CaV2 channel abundance and preference. We found that expression of CaV2.1 α1 subunit chimeras containing the CaV2.3 loop I-II region yielded similar presynaptic Ca2+ currents compared to the CaV2.1 α1 subunit. However, CaV2.3 loop II-III region or cytoplasmic C-terminus (CT) resulted in a large reduction of presynaptic Ca2+ currents compared to the CaV2.1 α1 subunit. Moreover, the Ca2+ current sensitivity to the CaV2.1 blocker Agatoxin-IVA, was the same between the chimeras and the CaV2.1 α1 subunit. Additionally, we found no reduction in presynaptic Ca2+ currents with CaV2.1/2.2 cytoplasmic loop I-II or CT chimeras. We conclude that the motifs in the CaV2.1 loop II-III and CT do not individually regulate CaV2.1 preference, but these motifs control CaV2.1 levels and the CaV2.3 CT contains motifs that negatively regulate presynaptic CaV2.3 levels. The CaV2 α1 subunit loop I-II regions do not regulate presynaptic CaV2 abundance. We propose that the motifs controlling presynaptic CaV2.1 preference are distinct from those regulating CaV2.1 levels and may act synergistically to impact pathways regulating CaV2.1 preference and abundance. Moreover, CaV2 subtype preference may be regulated by motifs in CaVβ or α2δ subunits since these subunits are indicated in controlling channel insertion. Identification of domains regulating CaV2.1 abundance and preference, and synaptic transmission is fundamental to understanding the molecular mechanisms controlling synaptic function that ensures high fidelity synaptic transmission during development of CNS.