title: Glycine release provoked by disturbed Na⁺, Na⁺ and Ca²⁺ homeostasis in cerebellar nerve endings: roles of Ca²⁺ channels, Na⁺/Ca²⁺ exchangers and GlyT2 transporter reversal.
abstract: Glycine release provoked by ion dysregulations typical of some neuropathological conditions was analyzed in cerebellar synaptosomes selectively pre-labelled with [³H]glycine through GlyT2 transporters and exposed in superfusion to KCl, 4-aminopyridine (4-AP) or veratridine. The overflows caused by relatively low concentrations of the releasers were largely external Ca²⁺-dependent. Higher concentrations of KCl (50 mM) or veratridine (10 μM), but not of 4-AP (1 mM), involved also external Ca²⁺-independent mechanisms. GlyT1-mediated release could not be observed; only the external Ca²⁺-independent veratridine-evoked overflow occurred significantly by GlyT2 reversal. None of the three depolarizing agents activated store-operated or transient receptor potential or L-type Ca²⁺ channels. The overflows caused by KCl or 4-AP occurred in part by N- and P/Q-type voltage-sensitive calcium channel-dependent exocytosis. Significant portions of the external Ca²⁺-dependent overflow evoked by KCl or 4-AP (and all that caused by veratridine) were mediated by reverse plasmalemmal Na⁺/Ca²⁺ exchangers. Significant contribution to the overflows evoked by KCl or veratridine came from Ca²⁺ originated through mitochondrial Na⁺/Ca²⁺ exchangers. Ca²⁺-induced Ca²⁺ release (CICR) mediated by inositoltrisphosphate receptors (InsP₃Rs) represents the final trigger of the glycine release evoked by high KCl. The overflows evoked by 4-AP or, less so, by veratridine also involved InsP₃R-mediated CICR and, in part, CICR mediated by ryanodine receptors. To conclude, ionic dysregulations typical of ischemia and epilepsy caused glycine release in cerebellum by multiple differential mechanisms that may represent potential therapeutic targets.
authors.affiliation: Department of Experimental Medicine, Section of Pharmacology and Toxicology, Genova, Italy.
authors.forename: Cristina
authors.initials: C
authors.lastname: Romei
authors.forename: Silvia
authors.initials: S
authors.lastname: Di Prisco
authors.forename: Maurizio
authors.initials: M
authors.lastname: Raiteri
authors.forename: Luca
authors.initials: L
authors.lastname: Raiteri
mesh_terms: D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D001549:Benzamides / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002531:Cerebellum / Q000166:cytology / Q000378:metabolism*; D005089:Exocytosis / Q000187:drug effects; D005998:Glycine / Q000378:metabolism*; D050487:Glycine Plasma Membrane Transport Proteins / Q000378:metabolism*; D006706:Homeostasis / Q000187:drug effects / Q000502:physiology*; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000187:drug effects; D008297:Male; D051379:Mice; D018613:Microscopy, Confocal; D009411:Nerve Endings / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger / Q000378:metabolism*; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism; D014701:Veratridine / Q000494:pharmacology
chemical_list: C532849:4-benzyloxy-3,5-dimethoxy-N-(1-(dimethylaminocyclopently)methyl)benzamide; D001549:Benzamides; D015220:Calcium Channels; D050487:Glycine Plasma Membrane Transport Proteins; D053496:Inositol 1,4,5-Trisphosphate Receptors; D026902:Potassium Channel Blockers; C493270:Slc6a5 protein, mouse; D019831:Sodium-Calcium Exchanger; D011189:Potassium Chloride; D014701:Veratridine; D012964:Sodium; D015761:4-Aminopyridine; D011188:Potassium; D002118:Calcium; D005998:Glycine