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Depletion of calcium in the synaptic cleft of a calyx‐type synapse in the rat brainstem
Author(s) -
Borst J. G. G.,
Sakmann B.
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.00123.x
Subject(s) - postsynaptic potential , excitatory postsynaptic potential , neurotransmission , depolarization , post tetanic potentiation , neuroscience , chemistry , inhibitory postsynaptic potential , synaptic augmentation , trapezoid body , postsynaptic current , biophysics , calcium , synaptic plasticity , excitatory synapse , synaptic cleft , biology , brainstem , biochemistry , receptor , organic chemistry
1 A new form of synaptic depression of excitatory synaptic transmission was observed when making voltage‐clamp recordings from large presynaptic terminals, the calyces of Held and postsynaptic cells, the principal cells of the medial nucleus of the trapezoid body (MNTB), in slices of the rat auditory brainstem. 2 A short (100 ms) depolarization of the postsynaptic cell to 0 mV reduced the amplitude of the EPSCs by 35 ± 5% ( n = 7) , measured at 10 ms following the depolarization. Recovery occurred within 0·5 s. 3 The reduction of the EPSCs was most probably due to reduced presynaptic calcium influx, since postsynaptic depolarization reduced presynaptic calcium or barium currents. Conversely, presynaptic depolarization also reduced postsynaptic calcium or barium influx, under conditions where transmitter release was minimal. 4 The calcium currents and the postsynaptic depolarization‐induced suppression of synaptic transmission recovered with a similar time course, suggesting that this form of synaptic depression was, most probably, due to depletion of Ca 2+ in the synaptic cleft. 5 We conclude that when the Ca 2+ influx into the pre‐ or postsynaptic cell is large, extracellular Ca 2+ is depleted. Under these conditions, the Ca 2+ concentration in the synaptic cleft is a sensitive indicator of the level of synaptic activity. However, the synaptic cleft is less sensitive to Ca 2+ depletion than predicted from its estimated volume.