Depletion and Replenishment of Vesicle Pools at a Ribbon-Type Synaptic Terminal

摘要: Synaptic depression was studied using capacitance measurements in synaptic terminals of retinal bipolar neurons. Single 250 msec depolarizations evoked saturating responses averaging ∼150 fF, whereas trains produced plateau increases ∼300 fF. Both types stimuli were followed by pronounced depression, which recovered with a time constant ∼8 sec after single pulses but required >20 for full recovery pulse trains. Inactivation presynaptic calcium current could not account is attributed instead to depletion releasable and reserve vesicle pools that are recruited replenished at different rates. Recovery from normal the absence fast endocytosis, suggesting replenishment pool preformed vesicles rather than preferential recycling recently fused vesicles. Given vivo light response class neuron here, it likely that, under least some illumination conditions, cells produce phasic bout exocytosis tonic release.