Nicotine-induced and depolarisation-induced glutamate release from hippocampus mossy fibre synaptosomes: two distinct mechanisms.
Hippocampus mossy fibre terminals activate CA3 pyramidal neurons via two distinct mechanisms, both quantal and glutamatergic: (i) rapid excitatory transmission in response to afferent action potentials and (ii) delayed and prolonged release following nicotinic receptor activation. These processes were analysed here using rat hippocampus mossy fibres synaptosomes. The relationships between synaptosome depolarisation and glutamate release were established in response to high-KCl and gramicidin challenges. Half-maximal release corresponded to a 52 mV depolarisation step. KCl-induced release was accompanied by transient dissipation of the proton gradient across synaptic vesicle membrane. Nicotine elicited a substantial glutamate release from mossy fibre synaptosomes (EC(50) 3.14 microM; V(max) 12.01 +/- 2.1 nmol glutamate/mg protein; Hill's coefficient 0.99). However, nicotine-induced glutamate release was not accompanied by any change in the membrane potential or in the vesicular proton gradient. The effects of acetylcholine (200 microM) were similar to those of nicotine (25 microM). Nicotinic alpha7 receptors were evidenced by immuno-cytochemistry on the mossy fibre synaptosome plasma membrane. Therefore, the same terminals can release glutamate in response to two distinct stimuli: (i) rapid neurotransmission involving depolarisation-induced activation of voltage-gated Ca(2+) channels and (ii) a slower nicotinic activation which does not involve depolarisation or dissipation of the vesicular proton gradient.
Bancila
Victor
V
Département des Neurosciences fondamentales, Université de Genève, Centre Médical Universitaire, Switzerland.
Cordeiro
J Miguel
JM
Bloc
Alain
A
Dunant
Yves
Y
D000818:Animals; D016764:Cell Polarity / Q000187:drug effects* / Q000502:physiology*; D018698:Glutamic Acid / Q000378:metabolism*; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D019599:Mossy Fibers, Hippocampal / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D009538:Nicotine / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D011978:Receptors, Nicotinic / Q000378:metabolism; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D064569:alpha7 Nicotinic Acetylcholine Receptor
C579165:Chrna7 protein, rat; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; D018698:Glutamic Acid; D009538:Nicotine