Characterization of the release of cholecystokinin-8 from isolated nerve terminals and comparison with exocytosis of classical transmitters.
In the present study, the release of the neuropeptide cholecystokinin-8 (CCK) from purified nerve terminals (synaptosomes) of the rat hippocampus was characterized with respect to the subcellular distribution, the release upon addition of various agents, the release kinetics, the Ca2+ and ATP dependence of release, and the relationship between CCK release and elevations of intraterminal free Ca2+ concentration ([Ca]i). These characteristics were compared with those for the release of classical transmitters in similar preparations. CCK-like immunoreactivity (CCK-LI) is enriched in the purified synaptosomal fraction of hippocampus homogenates and released in a strictly Ca2(+)-dependent manner upon chemical depolarization, addition of 4-aminopyridine, or stimulation with the Ca2+ ionophore ionomycin. The presence of Ca2+ in the medium significantly stimulates the basal efflux of CCK-LI from synaptosomes. The release upon stimulation develops gradually in time with no significant release in the first 10 s and levels off after 3 min of depolarization. At this time, a large amount of CCK-LI is still present inside the synaptosomes. A correlation exists between the release of CCK-LI and the elevations of [Ca]i. The release of CCK-LI is decreased, but not blocked, upon ATP depletion. These characteristics markedly differ from those for classical transmitters, which show a fast component of Ca2(+)-dependent (exocytotic) release, an absolute dependence on cellular ATP, and no marked stimulation of basal efflux in the presence of Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)
Verhage
M
M
Department of Experimental Zoology, University of Amsterdam, The Netherlands.
Ghijsen
W E
WE
Nicholls
D G
DG
Wiegant
V M
VM
D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D004305:Dose-Response Relationship, Drug; D005089:Exocytosis; D007700:Kinetics; D008297:Male; D009411:Nerve Endings / Q000378:metabolism*; D018377:Neurotransmitter Agents / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains; D012844:Sincalide / Q000378:metabolism*; D013574:Synaptosomes / Q000378:metabolism
D018377:Neurotransmitter Agents; D000255:Adenosine Triphosphate; D012844:Sincalide; D011188:Potassium