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Heterogeneous presynaptic Ca 2+ channel types triggering GABA release onto medial preoptic neurons from rat
Author(s) -
Haage David,
Karlsson Urban,
Johansson Staffan
Publication year - 1998
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.1469-7793.1998.077bu.x
Subject(s) - postsynaptic potential , bicuculline , biophysics , chemistry , reversal potential , depolarization , neurotransmission , postsynaptic current , channel blocker , neuroscience , electrophysiology , gabaa receptor , patch clamp , receptor , biology , calcium , biochemistry , organic chemistry
1 Voltage‐dependent Ca 2+ channels triggering GABA release onto neurons from the medial preoptic nucleus of rat were investigated. Acutely dissociated neurons with adherent functional synaptic terminals were investigated by tight‐seal whole‐cell recordings from the postsynaptic cells. 2 Spontaneous current events similar to miniature postsynaptic currents were recorded. They were blocked by bicuculline (100 μM), showed a roughly unimodal amplitude distribution and a reversal potential consistent with a Cl − current, and were therefore attributed to GABA A receptors activated by synaptically released GABA. 3 Application of 140 mM KCl, expected to depolarize presynaptic terminals, evoked currents that were ascribed to a more massive release of GABA. The KCl‐induced synaptic currents were abolished in Ca 2+ ‐free solutions and showed a roughly hyperbolic relation to external Ca 2+ concentration with half‐saturation at 0.15 m m . They further depended on the concentration of applied KCl in a way expected for high‐threshold Ca 2+ channels. 4 The KCl‐evoked synaptic currents were completely blocked by 200 μ m Cd 2+ , but only partially blocked by 200 μ m Ni 2+ . 5 The KCl‐evoked synaptic currents were insensitive to the L‐type Ca 2+ channel blocker nifedipine (10 μ m ). However, the synaptic currents were sensitive to either 1 μ m ω‐conotoxin GVIA, 25 n m ω‐agatoxin IVA or 1 μ m ω‐conotoxin MVIIC. 6 It was concluded that, in many presynaptic terminals, the Ca 2+ influx triggering GABA release onto medial preoptic neurons is mainly mediated by one predominant type of high‐ threshold Ca 2+ channel that may be either of N‐, P‐ or Q‐type. 7 It was further concluded that terminals with similar predominant channel types often were clustered on the same postsynaptic cell.