Characterization of the mGluR(1)-mediated electrical and calcium signaling in Purkinje cells of mouse cerebellar slices.
The metabotropic glutamate receptor 1 (mGluR(1)) plays a fundamental role in postnatal development and plasticity of ionotropic glutamate receptor-mediated synaptic excitation of cerebellar Purkinje cells. Synaptic activation of mGluR(1) by brief tetanic stimulation of parallel fibers evokes a slow excitatory postsynaptic current and an elevation of intracellular calcium concentration ([Ca2+](i)) in Purkinje cells. The mechanism underlying these responses has not been identified yet. Here we investigated the responses to synaptic and direct activation of mGluR(1) using whole cell patch-clamp recordings in combination with microfluorometric measurements of [Ca2+](i) in mouse Purkinje cells. Following pharmacological block of ionotropic glutamate receptors, two to six stimuli applied to parallel fibers at 100 Hz evoked a slow inward current that was associated with an elevation of [Ca2+](i). Both the inward current and the rise in [Ca2+](i) increased in size with increasing number of pulses albeit with no clear difference between the minimal number of pulses required to evoke these responses. Application of the mGluR(1) agonist (S)-3,5-dihydroxyphenylglycine (3,5-DHPG) by means of short-lasting (5-100 ms) pressure pulses delivered through an agonist-containing pipette positioned over the Purkinje cell dendrite, evoked responses resembling the synaptically induced inward current and elevation of [Ca2+](i). No increase in [Ca2+](i) was observed with inward currents of comparable amplitudes induced by the ionotropic glutamate receptor agonist AMPA. The 3,5-DHPG-induced inward current but not the associated increase in [Ca2+](i) was depressed when extracellular Na+ was replaced by choline, but, surprisingly, both responses were also depressed when bathing the tissue in a low calcium (0.125 mM) or calcium-free/EGTA solution. Thapsigargin (10 microM) and cyclopiazonic acid (30 microM), inhibitors of sarco-endoplasmic reticulum Ca2+-ATPase, had little effect on either the inward current or the elevation in [Ca2+](i) induced by 3,5-DHPG. Furthermore, the inward current induced by 3,5-DHPG was neither blocked by 1-[2-(4-methoxyphenyl)-2-[3-(4-methoxyphenyl)propoxy] ethyl-1H-imidazole, an inhibitor of store operated calcium influx, nor by nimodipine or omega-agatoxin, blockers of voltage-gated calcium channels. These electrophysiological and Ca2+-imaging experiments suggest that the mGluR(1)-mediated inward current, although mainly carried by Na+, involves influx of Ca2+ from the extracellular space.
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Laboratory for Neuronal Circuit Dynamics, Brain Science Institute, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
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Knöpfel
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D000818:Animals; D002118:Calcium / Q000493:pharmacokinetics; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D005998:Glycine / Q000031:analogs & derivatives / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D051379:Mice; D008813:Mice, Inbred ICR; D009553:Nimodipine / Q000494:pharmacology; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques; D011689:Purkinje Cells / Q000502:physiology*; D018094:Receptors, Metabotropic Glutamate / Q000502:physiology*; D012118:Resorcinols / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000201:enzymology; D012964:Sodium / Q000493:pharmacokinetics; D019284:Thapsigargin / Q000494:pharmacology
D002121:Calcium Channel Blockers; D004791:Enzyme Inhibitors; D018691:Excitatory Amino Acid Antagonists; D007093:Imidazoles; D007211:Indoles; D018094:Receptors, Metabotropic Glutamate; D012118:Resorcinols; C104077:metabotropic glutamate receptor type 1; D009553:Nimodipine; C079215:3,5-dihydroxyphenylglycine; D019284:Thapsigargin; D012964:Sodium; D000252:Calcium-Transporting ATPases; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole; D002118:Calcium; D005998:Glycine; C000543:cyclopiazonic acid