Cyclic ADP-ribose and calcium-induced calcium release regulate neurotransmitter release at a cholinergic synapse of Aplysia

摘要

Presynaptic injection of cyclic ADP-ribose (cADPR), a modulator of the ryanodine receptor, increased the postsynaptic response evoked by a presynaptic spike at an identified cholinergic synapse in the buccal ganglion of Aplysia californica.The statistical analysis of long duration postsynaptic responses evoked by square depolarizations of the voltage-clamped presynaptic neurone showed that the number of evoked acetylcholine (ACh) quanta released was increased following cADPR injection.Overloading the presynaptic neurone with cADPR led to a transient increase of ACh release followed by a depression.cADPR injections did not modify the presynaptic Ca2+ current triggering ACh release.Ca2+ imaging with the fluorescent dye rhod-2 showed that cADPR injection rapidly increased the free intracellular Ca2+ concentration indicating that the effects of cADPR on ACh release might be related to Ca2+ release from intracellular stores.Ryanodine and 8-amino-cADPR, a specific antagonist of cADPR, decreased ACh release.ADP-ribosyl cyclase, which cyclizes NAD+ into cADPR, was present in the presynaptic neurone as shown by reverse transcriptase-polymerase chain reaction experiments.Application of NAD+, the substrate of ADP-ribosyl cyclase, increased ACh release and this effect was prevented by both ryanodine and 8-amino-cADPR.These results support the view that Ca2+-induced Ca2+ release might be involved in the build-up of the Ca2+ concentration which triggers ACh release, and thus that cADPR might have a role in transmitter release modulation.