La liberación de calcio de los depósitos intracelulares promueve la secreción de serotonina en terminales sinápticas

SUMMARY This work analyses the role of intracellular calcium pools in serotonin release from nerve terminals. Experiments were carried out in synapses formed in culture between serotonergic Retzius neurones and pressure mechanosensory neurons, isolated from the Central Nervous System of the leech. In this configuration, serotonin is released from clear vesicles at synapses or from extrasynaptic dense core vesicles. Locking ryanodine receptors in a sub-conductance state by incubation with 100 μM ryanodine caused an elongation of the synaptic potential in response to a presynaptic action potential or to trains of them, suggesting that calcium released from the endoplasmic reticulum through these channels reaches the synaptic vesicles and may promote their fusion with the plasma membrane. By contrast, depletion of intracellular calcium pools by incubation with 500 nM thapsigargin gradually decreased paired-pulse synaptic facilitation and abolished extrasynaptic axonal serotonin release in response to trains of impulses. All this occurred without changes in the properties of the postsynaptic membrane, indicating that intracellular calcium release participates in a feedback mechanism that enhances presynaptic and perisynaptic release in serotonergic neurons.