Adenosine suppresses exocytosis from cone terminals of the salamander retina

Abstract

In the retina, adenosine is released in the dark and has been shown to inhibit Ca 2+ influx through voltage-gated Ca 2+ channels in cones. Therefore, we tested whether adenosine can inhibit exocytosis from isolated cone photoreceptors. Simultaneous measurements of membrane exocytosis and Ca 2+ were made from cones using the activity-dependent dye, Synaptored-C2, and the Ca 2+ indicator dye, Fluo-4. Adenosine suppressed exocytosis in cones, indicating that transmitter release is also reduced from cone terminals, and further supports an inhibitory mechanism for modulating transmitter release onto second-order neurons. Furthermore, this raises the possibility that adenosine might be neuroprotective for photoreceptors and second-order neurons by suppressing Ca 2+ levels in cones and reducing exocytosis of L-glutamate, respectively.

Extracellular ATP Hydrolysis Inhibits Synaptic Transmission by Increasing pH Buffering in the Synaptic Cleft

“…This implies that ATP hydrolysis and not ATP itself exerts an effect on the slow component of feedback. In addition, A2 receptors have been suggested to modulate photoreceptor function [42] – [44] . We excluded a possible role for adenosine by measuring feedback in the presence of the specific A2 receptor blocker, ZM 241385, at a similar concentration as used by Stella and co-workers ( Figure 6C ) [42] – [44] .…”

“…In addition, A2 receptors have been suggested to modulate photoreceptor function [42] – [44] . We excluded a possible role for adenosine by measuring feedback in the presence of the specific A2 receptor blocker, ZM 241385, at a similar concentration as used by Stella and co-workers ( Figure 6C ) [42] – [44] . In this condition, neither the feedback amplitude nor its kinetics were affected ( p >0.2; n = 4), indicating that A2 receptors do not mediate feedback.…”

Calcium channels in rat horizontal cells regulate feedback inhibition of photoreceptors through an unconventional GABA‐ and pH‐sensitive mechanism

“…Other reported modulators of photoreceptor Ca signalling include somatostatin (via sst2A receptors; Akopian et al 2000), adenosine (via A 2 receptors; Stella et al 2009), nitric oxide (Kurenny et al 1994; Straiker & Sullivan, 2003) and cannabinoids (via CB1 receptors; Fan & Yazulla, 2003; Jackman et al 2011). Application of a cocktail containing antagonists of somatostatin sst2A receptors, adenosine A 2 receptors and nitric oxide production had no effect on photoreceptor [Ca 2+ ] i (Fig.…”

Adenosine and autism: A spectrum of opportunities

“…In the auditory system adenosine receptors are found in cochlear tissues, and adenosine A 1 receptor expression in the cochlea has been shown to increase under auditory stress, perhaps serving a protective role (Ramkumar et al, 2004; Vlajkovic et al, 2007). In the visual system, adenosine suppresses exocytosis in retinal cone terminals by decreasing Ca 2+ channel activity, thus reducing light transduction, and is neuroprotective for both cones and rods (Stella et al, 2010). …”