Adaptation of Ca(2+)-triggered exocytosis in presynaptic terminals.
Rapid increases in Ca2+ concentration, produced by photolysis of caged Ca2+, triggered exocytosis in squid nerve terminals. This exocytosis was transient in nature, decaying with a time constant of approximately 30 ms. The decay could not be explained by a decline in presynaptic Ca2+ concentration, depletion of synaptic vesicles, or desensitization of postsynaptic receptors. Experiments in which Ca2+ was increased either in a series of steps or continuously at different rates suggested that the decay is caused by adaptation of the exocytotic Ca2+ receptor to higher levels of Ca2+. This adjustable sensitivity to Ca2+ represents a novel property of the triggering mechanism that can be used to evaluate molecular models of exocytosis. Adaptation can limit the amount of transmitter released by a nerve terminal and permit the speed of a presynaptic Ca2+ rise to serve as a critical determinant of synaptic efficacy.
Hsu
S F
SF
Department of Physiology, University of Wisconsin Medical School, Madison 53706, USA.
Augustine
G J
GJ
Jackson
M B
MB
D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D049832:Decapodiformes; D004594:Electrophysiology; D005089:Exocytosis / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D018377:Neurotransmitter Agents / Q000378:metabolism; D017729:Presynaptic Terminals / Q000502:physiology*; D012680:Sensitivity and Specificity; D013572:Synaptic Vesicles / Q000502:physiology; D013997:Time Factors
D018377:Neurotransmitter Agents; D002118:Calcium