Regulation of free intracellular calcium concentration following glutamate exposure in cultured hippocampal neurons

• Main Author: Limbrick, David Delmar
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2000
• Subjects: Neurology; Neurosciences; Pharmacology
• ISBN: 9780599793583; 0599793589

Excessive activation of neuronal glutamate receptors has been implicated in the pathophysiology of excitotoxic neuronal injuries such as stroke, seizures, and traumatic brain injury. In hippocampal neurons, excitotoxic glutamate exposure has been shown to result in an extended neuronal depolarization (END) as well as protracted elevations in free intracellular calcium [Ca 2+]i both of which correlated with subsequent excitotoxic neuronal cell death. In this research project, current and voltage clamp electrophysiology was used in conjunction with indo-1 and fura-2ff Ca2+ imaging to investigate the possibility that a common pathological mechanism underlies both of these sequelae of glutamate excitotoxicity. The findings presented in this dissertation indicate that excitotoxic glutamate exposure caused two major changes in neuronal Ca2+ physiology, a persistent influx of extracellular Ca2+ and functional impairment of neuronal Ca2+ sequestration/extrusion mechanisms. In addition to its contribution to glutamate-induced protracted [Ca2+]i elevations, the persistent Ca2+ influx caused END, as omission of extracellular Ca2+ after glutamate exposure resulted in rapid and complete repolarization of neuronal membrane potential. Termed I END, the persistent Ca2+ current was determined to be Ca2+-selective because removal of extracellular Na+ had no effect on IEND, and predicted shifts in the reversal potential of IEND were observed following changes in extracellular Ca2+ concentration. Pharmacological studies demonstrated that IEND was not mediated by any of the traditionally recognized routes of Ca2+ entry. IEND was however, blocked by the omission of extracellular Ca2+ or by the addition of ZnCl 2 in the post-glutamate period. The findings presented in this dissertation represent the first report of a persistent, Ca2+-selective current induced by excitotoxic neuronal injury. Given the critical relationship between END, protracted [Ca2+]i elevations, and excitotoxic neuronal cell death, the identification of this novel Ca 2+ current, IEND, may represent an important new target for therapeutic intervention in excitotoxicity-related neurological injury.