Differential release of amino acids, neuropeptides, and catecholamines from isolated nerve terminals.
We have investigated transmitter release from small and large dense-core vesicles in nerve terminals isolated from guinea pig hippocampus. Small vesicles are found in clusters near the active zone, and large dense-core vesicles are located at ectopic sites. The abilities of Ca2+ channel activation and uniform elevation of Ca2+ concentration (with ionophores) to evoke secretion of representative amino acids, catecholamines, and neuropeptides were compared. For a given increase in Ca2+ concentration, ionophore was less effective than Ca2+ channel activation in releasing amino acids, but not in releasing cholecystokinin-8. Titration of the average Ca2+ concentration showed that the Ca2+ affinity for cholecystokinin-8 secretion was higher than that for amino acids. Catecholamine release showed intermediate behavior. It is concluded that neuropeptide release is triggered by small elevations in the Ca2+ concentration in the bulk cytoplasm, whereas secretion of amino acids requires higher elevations, as produced in the vicinity of Ca2+ channels.
Verhage
M
M
Department of Experimental Zoology, University of Amsterdam, Netherlands.
McMahon
H T
HT
Ghijsen
W E
WE
Boomsma
F
F
Scholten
G
G
Wiegant
V M
VM
Nicholls
D G
DG
D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002395:Catecholamines / Q000378:metabolism*; D005089:Exocytosis / Q000502:physiology; D006168:Guinea Pigs; D008564:Membrane Potentials; D009411:Nerve Endings / Q000378:metabolism*; D009479:Neuropeptides / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism; D012844:Sincalide / Q000378:metabolism; D013574:Synaptosomes / Q000648:ultrastructure
D000596:Amino Acids; D002395:Catecholamines; D009479:Neuropeptides; D012844:Sincalide; D002118:Calcium; D009638:Norepinephrine