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YEAR : 2015

Analog modulation of spike-evoked transmission in CA3 circuits is determined by Kv1.1 channels in a time-dependent manner

AUTHORS : Bialowas A, Rama S, Zbili M, Marra V, Fronzaroli-Molinieres L, Ankri N, Carlier E, Debanne D.

JOURNAL : European Jounral of Neuroscience
Synaptic transmission usually depends on action potentials (APs) in an all-or-none (digital) fashion. Recent studies indicate however that subthreshold presynaptic depolarization may facilitate spike-evoked transmission, thus creating an analog modulation of spike-evoked synaptic transmission, also called analog-digital (AD) synaptic facilitation. Yet, the underlying mechanisms are unclear. We show here that AD facilitation at CA3-CA3 synapses is time-dependent and requires long presynaptic depolarization (5-10 sec) for its induction. This depolarization-induced AD facilitation
(d-ADF) is blocked by the specific Kv1.1 channel blocker dendrotoxin-K. Using fast voltage-imaging of the axon, we show that somatic depolarization used for induction of d-ADF broadened the action potential in the axon through inactivation of Kv1.1 channels. Somatic depolarization enhanced spike-evoked calcium signals in presynaptic terminals, but not basal calcium. In conclusion, axonal Kv1.1 channels determine glutamate release in CA3 neurons in a time-dependent manner through the control of presynaptic spike waveform