M channels containing KCNQ2 subunits modulate norepinephrine, aspartate, and GABA release from hippocampal nerve terminals.
KCNQ subunits encode for the M current (I(KM)), a neuron-specific voltage-dependent K+ current with a well established role in the control of neuronal excitability. In this study, by means of a combined biochemical, pharmacological, and electrophysiological approach, the role of presynaptic I(KM) in the release of previously taken up tritiated norepineprine (NE), GABA, and d-aspartate (d-ASP) from hippocampal nerve terminals (synaptosomes) has been evaluated. Retigabine (RT) (0.01-30 microm), a specific activator of I(KM), inhibited [3H]NE, [3H]d-ASP, and [3H]GABA release evoked by 9 mm extracellular K+ ([K+]e). RT-induced inhibition of [3H]NE release was prevented by synaptosomal entrapment of polyclonal antibodies directed against KCNQ2 subunits, an effect that was abolished by antibody preabsorption with the KCNQ2 immunizing peptide; antibodies against KCNQ3 subunits were ineffective. Flupirtine (FP), a structural analog of RT, also inhibited 9 mm [K+]e-induced [3H]NE release, although its maximal inhibition was lower than that of RT. Electrophysiological studies in KCNQ2-transfected Chinese hamster ovary cells revealed that RT and FP (10 microm) caused a -19 and -9 mV hyperpolarizing shift, respectively, in the voltage dependence of activation of KCNQ2 K+ channels. In the same cells, the cognition enhancer 10,10-bis(4-pyridinylmethyl)-9(10H)-anthracenone (XE-991) (10 microm) blocked KCNQ2 channels and prevented their activation by RT (1-10 microm). Finally, both XE-991 (10-100 microm) and tetraethylammonium ions (100 microm) abolished the inhibitory effect of RT (1 microm) on [3H]NE release. These findings provide novel evidence for a major regulatory role of KCNQ2 K+ channel subunits in neurotransmitter release from rat hippocampal nerve endings.
Martire
Maria
M
Institute of Pharmacology, School of Medicine, Catholic University of Sacred Heart, 00168 Rome, Italy.
Castaldo
Pasqualina
P
D'Amico
Monia
M
Preziosi
Paolo
P
Annunziato
Lucio
L
Taglialatela
Maurizio
M
D000631:Aminopyridines / Q000494:pharmacology; D000818:Animals; D000873:Anthracenes / Q000494:pharmacology; D000927:Anticonvulsants / Q000494:pharmacology; D001224:Aspartic Acid / Q000737:chemistry / Q000378:metabolism*; D016466:CHO Cells; D002219:Carbamates / Q000494:pharmacology; D006224:Cricetinae; D006624:Hippocampus / Q000737:chemistry / Q000378:metabolism; D051658:KCNQ2 Potassium Channel; D051659:KCNQ3 Potassium Channel; D008297:Male; D009638:Norepinephrine / Q000737:chemistry / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010655:Phenylenediamines / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D024642:Potassium Channels, Voltage-Gated; D017729:Presynaptic Terminals / Q000737:chemistry / Q000378:metabolism*; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D051381:Rats; D013574:Synaptosomes / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000737:chemistry / Q000378:metabolism*
C112297:10,10-bis(4-pyridinylmethyl)-9(10H)-anthracenone; D000631:Aminopyridines; D000873:Anthracenes; D000927:Anticonvulsants; D002219:Carbamates; D051658:KCNQ2 Potassium Channel; D051659:KCNQ3 Potassium Channel; C496915:Kcnq2 protein, rat; C496918:Kcnq3 protein, rat; D010655:Phenylenediamines; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D021122:Protein Subunits; C101866:ezogabine; D001224:Aspartic Acid; D005680:gamma-Aminobutyric Acid; C034161:flupirtine; D011188:Potassium; D009638:Norepinephrine