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Graded inhibitory synaptic transmission between leech interneurons: assessing the roles of two kinetically distinct

Andrei I Ivanov1, Ronald L Calabrese

  • 1Department of Biology, Emory University, Atlanta, GA 30322, USA. Andrei.Ivanov@emory.edu

Journal of Neurophysiology
|April 28, 2006
PubMed

Insights

Calcium channels in leech heart interneurons differentially control synaptic transmission. Rapidly activating calcium currents (ICaF) are more effective than slowly activating currents (ICaS) for graded transmission, impacting heartbeat regulation.

Area of Science:

  • Neuroscience
  • Synaptic Transmission
  • Calcium Channel Physiology

Background:

  • Leech heartbeat relies on reciprocally inhibitory interneurons with high- and low-threshold (HVA and LVA) Ca channels.
  • LVA Ca current comprises distinct rapid (ICaF) and slow (ICaS) components crucial for graded transmission and burst formation.

Purpose of the Study:

  • To differentiate the roles of ICaF and ICaS in synaptic transmission between heart interneurons.
  • To investigate the interaction and relative efficacy of ICaF and ICaS in mediating graded synaptic release.

Main Methods:

  • Utilized varied stimulation protocols and inorganic Ca channel blockers (e.g., Ni2+).
  • Separated the functional contributions of ICaF and ICaS to synaptic transmission.
  • Assessed effects on both graded and spike-mediated transmission.

Main Results:

  • Ca2+ influx via ICaF is more effective for synaptic release than via ICaS.
  • The rate of Ca2+ entry through LVA channels is critical for transmission.
  • 1 mM Ni2+ selectively blocked LVA currents and graded transmission, sparing spike-mediated transmission.
  • Both ICaF and ICaS contribute to a shared pool of releasable synaptic vesicles.

Conclusions:

  • Differential efficacy of ICaF and ICaS in Ca2+ influx underlies graded synaptic transmission.
  • The interplay between Ca2+ dynamics and vesicle availability governs inhibitory transmission strength.
  • Multichannel domains from ICaF and radial diffusion from ICaS interact at release sites to mediate graded transmission.

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