TY - JOUR T1 - A Reluctant Gating Mode of Glycine Receptor Channels Determines the Time Course of Inhibitory Miniature Synaptic Events in Zebrafish Hindbrain Neurons JF - The Journal of Neuroscience JO - J. Neurosci. SP - 2856 LP - 2870 DO - 10.1523/JNEUROSCI.18-08-02856.1998 VL - 18 IS - 8 AU - Pascal Legendre Y1 - 1998/04/15 UR - http://www.jneurosci.org/content/18/8/2856.abstract N2 - Miniature IPSCs (mIPSCs) recorded in the Mauthner (M)-cell of zebrafish larvae have a broad amplitude distribution that is attributable only partly to the functional heterogeneity of postsynaptic glycine receptors (GlyRs). The role of the kinetic properties of GlyRs in amplitude fluctuation was investigated using fast-flow application techniques on outside-out patches. Short applications of a saturating glycine concentration evoked outside-out currents with a biphasic deactivation phase as observed for mIPSCs, and they were consistent with a rapid clearance of glycine from the synaptic cleft. Patch currents declined slowly during continuous applications of 3 mm glycine, but the biphasic deactivation phase of mIPSCs cannot reflect a desensitization process because paired-pulse desensitization was not observed. The maximum open probability (Po) of GlyRs was close to 0.9 with 3 mm glycine. Analyses of the onset of outside-out currents evoked by 0.1 mm glycine are consistent with the presence of two equivalent binding sites with aKd of O.3-O.4 mm. Activation and deactivation properties of GlyRs were better described with a kinetic model, including two binding states, a doubly liganded open state, and a reluctant gating mode leading to another open state. The 20–80% rise time of mIPSCs was independent of their amplitude and is identical to that of outside-out currents evoked by the applications of a saturating concentration of glycine (>1 mm). These results support the hypothesis that GlyR kinetics determines the time course of synaptic events at M-cell inhibitory synapses and that large mIPSC amplitude fluctuations are mainly of postsynaptic origin. ER -