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Adenosine inhibits voltage‐dependent Ca 2+ influx in cone photoreceptor terminals of the tiger salamander retina
Author(s) -
Stella Salvatore L.,
Hu Wanda D.,
Vila Alejandro,
Brecha Nicholas C.
Publication year - 2007
Publication title -
journal of neuroscience research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.72
H-Index - 160
eISSN - 1097-4547
pISSN - 0360-4012
DOI - 10.1002/jnr.21210
Subject(s) - adenosine , biophysics , retina , synapse , depolarization , biology , axon , chemistry , neuroscience , microbiology and biotechnology , anatomy , biochemistry
Abstract Endogenous adenosine has already been shown to inhibit transmitter release from the rod synapse by suppressing Ca 2+ influx through voltage‐gated Ca 2+ channels. However, it is not clear how adenosine modulates the cone synapse. Cone photoreceptors, like rod photoreceptors, also possess L‐type Ca 2+ channels that regulate the release of L‐glutamate. To assess the impact of adenosine on Ca 2+ influx though voltage‐gated Ca 2+ channels in cone terminals, whole‐cell perforated‐patch clamp recording and Ca 2+ imaging with fluo‐4 were used on isolated cones and salamander retinal slices. Synaptic markers (VAMP and piccolo) and activity‐dependent dye labeling revealed that tiger salamander cone terminals contain a broad, vesicle‐filled cytoplasmic extension at the base of the somatic compartment, which is unlike rod terminals that contain one or more thin axons, each terminating in a large bulbous synaptic terminal. The spatiotemporal Ca 2+ responses of the cone terminals do not differ significantly from the Ca 2+ responses of the soma or inner segment like that observed in rods. Whole‐cell recording of cone I Ca and Ca 2+ imaging of synaptic terminals in cones demonstrate that adenosine inhibited both I Ca and the depolarization‐evoked Ca 2+ increase in cone terminals in a dose‐dependent manner from 1 to 50 μM. These results indicate that, as in rods, adenosine's ability to suppress voltage‐dependent Ca 2+ channels at the cone synapse will limit the amount of L‐glutamate released. Therefore, adenosine has an inhibitory effect on L‐glutamate release at the first synapse, which likely favors elevated adenosine levels in the dark or during dark‐adapted conditions. © 2007 Wiley‐Liss, Inc.