Abstract
Calcium regulation of neurotransmitter release is essential for maintenance of synaptic transmission. However, the temporal and spatial organization of Ca2+ dynamics that regulate synaptic vesicle (SV) release efficacy in sympathetic neurons is poorly understood. Here, we investigate the N-type Ca2+ channels-mediated kinetic structure of Ca2+ regulation of cholinergic transmission of sympathetic neurons. We measured the effect of Ca2+ chelation with fast 1,2-bis(2-aminophenoxy) ethane-tetraacetic acid (BAPTA) and slow ethyleneglycol-tetraacetic acid (EGTA) buffers on exocytosis, synaptic depression, and recovery of the readily releasable vesicle pool (RRP), after both single action potential (AP) and repetitive APs. Surprisingly, postsynaptic potentials peaking at ≈12 ms after the AP was inhibited by both rapid and slow Ca2+ buffers, suggesting that, in addition to the well-known fast Ca2+ signals at the active zone (AZ), slow Ca2+ signals at the peak of Ca2+ entry also contribute to paired-pulse or repetitive APs responses. Following single AP, discrete Ca2+-transient regulated synaptic depression in a rapid (<30 ms) and slow (<120 ms) phase. In contrast, following prolonged APs trains, synaptic depression was reduced by a slow Ca2+ signal regulation lasting >200 ms. Finally, after an AP burst, recovery of the RRP was mediated by an AP-dependent rapid Ca2+ signal, and the expansion of releasable SV number by an AP firing activity-dependent slow Ca2+ signal. These data indicate that local Ca2+ signals operating near Ca2+ sources in the AZ are organized into discrete fast and slow temporal phases that remodel exocytosis and short-term plasticity to ensure long-term stability in acetylcholine release efficacy.
- Calcium channels
- Calcium
- Recycling
- Molecular dynamics
- Structure-activity relationships and modeling
- Patch clamp methods
- Regulation - physiological
- Exocytosis
- Synaptic plasticity
- The American Society for Pharmacology and Experimental Therapeutics