Using native plasma membrane vesicle suspensions from the rat cerebral cortex under conditions designed to alter intravesicular [Ca2+], we found that Ca2+ induced 47±5% more influx of [3H]GABA, [3H]D-aspartate and [3H]glycine at 37°C with half-times 1.7±0.5 1.3±0.4 and 1.3±0.4 min, respectively. We labelled GABA transporter sites with the uptake inhibitor, [3H]-(R,S)-N-[4,4-bis(3-methyl-2-thienyl)but-3-en-l-yl]nipecotic acid and found that Ca2+ induced a partial dissociation of the bound inhibitor from GABA transporter sites with a similar half-time. By means of rapid kinetic techniques applied to native plasma membrane vesicle suspensions, containing synaptic vesicles stained with the amphipathic fluorescent styryl membrane probe N-(3-triethylammoniumpropyl)-4-[4-(dibutylamino)styryl]pyridinium dibromide, we have measured the progress of the release and reuptake of synaptic vesicles in response to Ca2+ and high-[K+] depolarization in the 0.0004-100 s range of time. Synaptic vesicle exocytosis, strongly influenced by external [Ca2+], appeared with the kinetics accelerated by depolarization. These results are consistent with the potential involvement of Ca2+ in taking low-affinity transporters to the plasma membrane surface via exocytosis.
ASJC Scopus subject areas
- Cellular and Molecular Neuroscience
- Cell Biology