April 2011
Volume 52, Issue 14
Free
ARVO Annual Meeting Abstract  |   April 2011
Light, Adenosine Transporters, And Ecto-nucleotidases Contribute To Adenosine Levels In The Outer Retina
Author Affiliations & Notes
  • Salvatore L. Stella, Jr.
    Basic Med Sciences and Ophthalmology, University of Missouri Kansas City, Kansas City, Missouri
  • Nicholas Dale
    Biological Sciences, University of Warwick, Coventry, United Kingdom
  • Jean Sevigny
    Centre de recherche en Rhumatologie et Immunologie, Centre Hospitalier Universitaire de Québec, Université Laval, Quebec City, Quebec, Canada
  • Footnotes
    Commercial Relationships  Salvatore L. Stella, Jr., None; Nicholas Dale, None; Jean Sevigny, None
  • Footnotes
    Support  Vision Research Foundation of Kansas City (SLS); Wellcome Trust (ND);Canadian Institutes of Health Research (CIHR) and Fonds de Recherche en Santé du Québec (FRSQ) (JS)
Investigative Ophthalmology & Visual Science April 2011, Vol.52, 4115. doi:
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      Salvatore L. Stella, Jr., Nicholas Dale, Jean Sevigny; Light, Adenosine Transporters, And Ecto-nucleotidases Contribute To Adenosine Levels In The Outer Retina. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4115.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose: : Previous work in our laboratory has shown that endogenous adenosine levels suppress transmitter release from photoreceptors. Interestingly, adenosine levels are influenced by conditions of illumination as well as by adenosine transporters. However, it is not known how adenosine levels are regulated in the outer retina. The goal of this study was to investigate the effect of light, adenosine transporters, and the distribution of enzymes involved in the regulation of adenosine in the outer retina.

Methods: : Experiments were performed in preparations from mice and larval tiger salamanders. [Ca2+]i levels were measured from photoreceptors using either fura-2/AM or fluo-4/AM. Whole cell patch-clamp recordings were used to measure photoreceptor calcium currents (ICa) and light-evoked currents in second-order neurons to assess transmitter release. Adenosine measurements were made using adenosine biosensors with a potentiostat. Antibodies to nucleoside triphosphate diphosphohydrolase-1 (NTPDase1), -2, and -3 were used to map the localization of purine metabolism in the outer retina.

Results: : Light stimulation suppressed endogenous adenosine levels in dark-adapted retina, which partially recovered. Low levels of adenosine release could be detected with elevated K+, however stimulation with glutamate receptor agonists (AMPA/Kainate) showed no significant change in basal adenosine levels. Adenosine release was partially decreased following the removal of extracellular Ca2+, implying some Ca2+-dependent release. Adenosine transport blockers caused an increase in extracellular adenosine, suppressed synaptic transmission onto second-order neurons, and inhibited photoreceptor voltage-dependent Ca2+ influx, suggesting that adenosine transporters remove adenosine from the synapse. Ecto-nucleotidases (NTPDase 1 and NTPDase 2) were highly expressed at photoreceptors terminals.

Conclusions: : Our findings indicate that adenosine levels are tightly regulated by conditions of illumination and ecto-nucleotidases in and around photoreceptor terminals. These findings highlight the important and dynamic light-modulated nature of adenosine on transmitter release in the retina and provide a novel way to regulate both the excitability and tonic release of L-glutamate from photoreceptors.

Keywords: adenosine • retina: distal (photoreceptors, horizontal cells, bipolar cells) • retinal connections, networks, circuitry 
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