Analysis of Adenosine Immunoreactivity, Uptake, and Release in Purified Cultures of Developing Chick Embryo Retinal Neurons and Photoreceptors

Abstract: We have investigated the presence of endogenous adenosine and of mechanisms for adenosine uptake and release in chick embryo retinal neurons and photoreceptors grown in purified cultures in the absence of glial cells. Simultaneous autoradiographic and immunocytochemical analysis showed that endogenous adenosine and the uptake mechanism for this nucleoside colocalize in practically all the photoreceptors, but only in ∼20% of the neurons. Approximately 25% of the neurons showed either immunocytochemical labeling or autoradiographic labeling, while >50% of the neurons were unlabeled with both techniques. [³H]Adenosine uptake was saturable and could be inhibited by nitrobenzylthioinosine and dipyridamole and by pretreatment of the [³H]adenosine with adenosine deaminase. Although these observations indicate that the uptake is specific for adenosine, only 35% of accumulated radioactivity was associated with adenosine, with the remaining 65% representing inosine, hypoxanthine. and nucleotides plus uric acid. Adenosine as well as several of its metabolites were released by the cells under basal as well as K⁺‐stimulated conditions. Potassium‐enhanced release was blocked by 10 mM CoCl₂ or in Ca²⁺‐free, Mg²⁺‐rich solutions. The results indicate that retinal cells that synthesize, store, and release adenosine differentiate early during embryogenesis and are therefore consistent with a hypothetical role for adenosine in retinal development.