title: Ca2+ ion permeability and single-channel properties of the metabotropic slow EPSC of rat Purkinje neurons.
abstract: The slow EPSC (sEPSC) of cerebellar parallel fiber --> Purkinje neuron synapses is mediated by metabotropic glutamate receptor type 1 (mGluR1) activation of nonselective cation channels. Here, the channel properties were studied with uniform calibrated photorelease of L-glutamate with ionotropic receptors blocked, allowing isolation of postsynaptic processes, or with parallel fiber stimulation or mGluR1 agonist application. Evoked current and fluorescence from Ca(2+) indicators were recorded. Noise analysis of the mGluR1 current gave a single-channel conductance of 0.6 pS and showed low open probability at maximal mGluR1 activation. Similar small single-channel conductances were obtained with the mGluR1 agonist (S)-dihydroxyphenylglycine, with parallel fiber or climbing fiber stimulation. The mGluR1 current fluctuations were unaffected by potassium channel blockers. Photoreleased L-glutamate triggered a Ca(2+) concentration increase in the distal dendrites with a time course similar to that of the mGluR1 current. The proximal dendritic and somatic Ca(2+) changes were delayed with respect to the current. Ca(2+) channel blockers and the phospholipase Cdelta inhibitor 1-[6-[((17delta)-3-methoxyestra-1,3,5[10]-trien-17-yl)amino]hexyl]-1H-pyrrole-2,5-dione, which inhibits mGluR1-activated intracellular Ca(2+) release, did not prevent the dendritic Ca(2+) concentration increase. Polyamine naphthylacetyl spermine and cationic adamantanes that block the pore of the channel were used to vary the mGluR1 current over a wide range in each cell but still at maximal mGluR1 activation. The Ca(2+) influx was inhibited in parallel with the current. The results show that the mGluR1-activated current and the sEPSC are attributable to small-conductance, low-open probability Ca(2+)-permeable cation channels that will mediate spine-specific Ca(2+) influx during the parallel fiber sEPSP.
authors.affiliation: National Institute for Medical Research, London NW7 1AA, United Kingdom.
authors.forename: Marco
authors.initials: M
authors.lastname: Canepari
authors.forename: Céline
authors.initials: C
authors.lastname: Auger
authors.forename: David
authors.initials: D
authors.lastname: Ogden
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000502:physiology; D002531:Cerebellum / Q000166:cytology / Q000378:metabolism / Q000502:physiology; D004558:Electric Stimulation; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology*; D005971:Glutamates / Q000378:metabolism / Q000494:pharmacology; D066298:In Vitro Techniques; D007211:Indoles / Q000378:metabolism / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D010777:Photochemistry; D011689:Purkinje Cells / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D018094:Receptors, Metabotropic Glutamate / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: C488057:2-amino-5-(5-((methoxycarbonyl)methyl)-7-nitroindol-1-yl)-5-oxopentanoic acid; C440256:4-methoxy-7-nitroindolinyl-glutamate; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D005971:Glutamates; D007211:Indoles; D007473:Ion Channels; D018094:Receptors, Metabotropic Glutamate; C104077:metabotropic glutamate receptor type 1; D002118:Calcium