Matching kinetics of synaptic vesicle recycling and enhanced neurotransmitter influx by Ca2+ in brain plasma membrane vesicles

Using native plasma membrane vesicle suspensions from the rat cerebral cort ex under conditions designed to alter intravesicular [Ca2+], we found that Ca2+ induced 47+/-5% more influx of [H-3]GABA, [H-3]D-aspartate and [H-3]gl ycine at 37 degrees 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 i nhibitor, [H-3]-(R,S)-N-[4,4-bis(3-methyl-2-thienyl)but-3-en-1-yl]nipecotic acid and found that Ca2+ induced a partial dissociation of the bound inhib itor from GABA transporter sites with a similar half-time. By means of rapi d kinetic techniques applied to native plasma membrane vesicle suspensions, containing synaptic vesicles stained with the amphipathic fluorescent styr yl membrane probe N-(3-triethylammoniumpropyl)-4-[4- (dibutylamino)styryl]p yridinium dibromide, we have measured the progress of the release and reupt ake of synaptic vesicles in response to Ca2+ and high-[K+] depolarization i n the 0.0004-100 s range of time. Synaptic vesicle exocytosis, strongly inf luenced by external [Ca2+], appeared with the kinetics accelerated by depol arization. These results are consistent with the potential involvement of C a2+ in taking low-affinity transporters to the plasma membrane surface via exocytosis. (C) 1998 Elsevier Science Ltd. All rights reserved.