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Transmitter Glutamate Release from Isolated Nerve Terminals: Evidence for Biphasic Release and Triggering by Localized $Ca^{2+}$
| Content Provider | Scilit |
|---|---|
| Author | McMahon, Harvey T. Nicholls, David G. |
| Copyright Year | 1991 |
| Description | Journal: Journal of Neurochemistry The kinetics of $Ca^{2+}$-dependent release of glutamate from guinea-pig cerebrocortical synaptosomes evoked by KCl or 4-aminopyridine are investigated using a continuous flu-orimetric assay. Release by both agents is biphasic, with a rapid phase complete within 2 s followed by a more extensive slow phase with a half-maximal release in 52 s for KCl-evoked release and > 120 s for 4-aminopyridine-evoked release. The two phases ofglutamate release may reflect a dual localization of releasable vesicles at the active zone and in the bulk cytoplasm. Decreasing depolarization depresses the extent rather than increasing the time for half-maximal $Ca^{2+}$-dependent release. Both the fast and the slow phases of glutamate release require external $Ca^{2+}$ and cytoplasmic ATP. KCl depolarization produces a transient “spike”of cytoplasmic free $Ca^{2+}$ ([Ca^{2+}$]_{c}$), which recovers to a plateau; the major component of glutamate release occurs during this plateau. Predepolarization in the absence of added external $Ca^{2+}$, to inhibit transient $Ca^{2+}$ channels, does not affect the subsequent glutamate release evoked by $Ca^{2+}$ readdition. Thus, release involves primarily noninactivating $Ca^{2+}$ channels. For a given increase in [Ca^{2+}$]_{c}$, KCl and 4-aminopyridine cause equal release of glutamate, while ionomycin releases much less glutamate. This lowered efficiency is not due to ATP depletion. It is concluded that glutamate exocytosis is evoked by localized $Ca^{2+}$ entering through noninactivating voltage-dependent $Ca^{2+}$ channels and that nonlocalized $Ca^{2+}$ entry with ionomycin is inefficient. |
| Related Links | https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1471-4159.1991.tb02566.x |
| Ending Page | 94 |
| Page Count | 9 |
| Starting Page | 86 |
| e-ISSN | 14714159 |
| DOI | 10.1111/j.1471-4159.1991.tb02566.x |
| Journal | Journal of Neurochemistry |
| Issue Number | 1 |
| Volume Number | 56 |
| Language | English |
| Publisher | Wiley-Blackwell |
| Publisher Date | 1991-01-01 |
| Access Restriction | Open |
| Subject Keyword | Journal: Journal of Neurochemistry Localized Calcium |
| Content Type | Text |
| Resource Type | Article |
