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The Journal of Neuroscience, April 7, 2004, 24(14):3563-3573; doi:10.1523/JNEUROSCI.5374-03.2004

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Cellular/Molecular
Ca²⁺ Ion Permeability and Single-Channel Properties of the Metabotropic Slow EPSC of Rat Purkinje Neurons

Marco Canepari,¹ Céline Auger,^1,2 and David Ogden¹

¹National Institute for Medical Research, London NW7 1AA, United Kingdom, and ²Laboratoire de Physiologie Cérébrale, Unité Mixte de Recherche 8118, Université Paris V, Paris 75006, France

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 Ca²⁺ 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 Ca²⁺ concentration increase in the distal dendrites with a time course similar to that of the mGluR1 current. The proximal dendritic and somatic Ca²⁺ changes were delayed with respect to the current. Ca²⁺ channel blockers and the phospholipase C inhibitor 1-[6-[((17)-3-methoxyestra-1,3,5[10]-trien-17-yl)amino]hexyl]-1H-pyrrole-2,5-dione, which inhibits mGluR1-activated intracellular Ca²⁺ release, did not prevent the dendritic Ca²⁺ 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 Ca²⁺ 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 Ca²⁺-permeable cation channels that will mediate spine-specific Ca²⁺ influx during the parallel fiber sEPSP.

Key words: calcium; cerebellum; channel; EPSP; Purkinje cell; synaptic

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Received Dec 5, 2003; revised February 4, 2004; accepted February 21, 2004.

This article has been cited by other articles:

				J. H. Shin, Y. S. Kim, and D. J. Linden Dendritic glutamate release produces autocrine activation of mGluR1 in cerebellar Purkinje cells PNAS, January 15, 2008; 105(2): 746 - 750. [Abstract] [Full Text] [PDF]

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