Spike-mediated and graded inhibitory synaptic transmission between leech interneurons: evidence for shared release sites

Journal of Neurophysiology
Andrei I Ivanov, Ronald L Calabrese

Abstract

Inhibitory synaptic transmission between leech heart interneurons consist of two components: graded, gated by Ca2+ entering by low-threshold [low-voltage-activated (LVA)] Ca channels and spike-mediated, gated by Ca2+ entering by high-threshold [high-voltage-activated (HVA)] Ca channels. Changes in presynaptic background Ca2+ produced by Ca2+ influx through LVA channels modulate spike-mediated transmission, suggesting LVA channels have access to release sites controlled by HVA channels. Here we explore whether spike-mediated and graded transmission can use the same release sites and thus how Ca2+ influx by HVA and LVA Ca channels might interact to evoke neurotransmitter release. We recorded pre- and postsynaptic currents from voltage-clamped heart interneurons bathed in 0 mM Na+/5 mM Ca2+ saline. Using different stimulating paradigms and inorganic Ca channel blockers, we show that strong graded synaptic transmission can occlude high-threshold/spike-mediated synaptic transmission when evoked simultaneously. Suppression of LVA Ca currents diminishes graded release and concomitantly increases the ability of Ca2+ entering by HVA channels to release transmitter. Uncaging of Ca chelator corroborates that graded release occludes spike-...Continue Reading

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Jan 26, 2012·Science Signaling·Arnulfo TorresMaiken Nedergaard
Jun 30, 2006·Journal of Neurophysiology·Rodolfo J Haedo, Jorge Golowasch
Jul 17, 2009·Journal of Neurophysiology·Bjoern Ch LudwarElizabeth C Cropper
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Oct 1, 2011·The Journal of Neuroscience : the Official Journal of the Society for Neuroscience·Shunbing ZhaoFarzan Nadim
Sep 15, 2007·Journal of Neurophysiology·Andrey V Olypher, Ronald L Calabrese

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