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AT E Hartwick, WH Baldridge; Adenosine Modulates Glutamate-Induced Calcium Influx in Retinal Neurons . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4752.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: There is considerable evidence that adenosine acts as a neuromodulator in the central nervous system. Although adenosine receptors (A1 and A2) have been identified in the retina, adenosine's role here is not fully understood. The purpose of this work is to investigate the action of adenosine on the glutamate-induced calcium influx in isolated rat retinal neurons. Methods: Retinae were obtained from neonatal rats and dissociated enzymatically into a suspension of single cells. The retinal cells were cultured in serum-free medium containing neurotrophic factors and forskolin. After four to nine days in culture, the cells were loaded with the ratiometric calcium-indicator dye Fura-2 and exposed to a short application (30 s) of 10 micromolar glutamate, both with and without the presence of 100 micromolar adenosine or 1 micromolar CHA (an A1 agonist). Changes in fluorescence at 340 and 380 nm were monitored, and the resulting ratio was used to determine changes in intracellular calcium levels. Results: In the majority of retinal neurons (84% of the total number of neurons imaged), adenosine did not modulate the glutamate-induced calcium influx. However, in one subpopulation of neurons (9% of the total number), the glutamate-induced calcium influx was repeatedly increased when adenosine was present, while in another group (7% of the total) the influx was repeatedly decreased by adenosine. In the former group, the mean increase in the peak Fura-2 ratio was 15.7 +/- 3.1%, and in the latter group, the mean decrease was 16.3 +/- 1.8%. In presence of CHA, only the subset of neurons with a decreased response to glutamate were evident, suggesting that the inhibitory effect of adenosine is mediated through the A1 receptor. Conclusion: This work shows that adenosine can affect the glutamate-induced calcium influx in certain populations of retinal neurons, and provides evidence that adenosine can function as a neuromodulator in the retina. Adenosine can either increase or decrease the calcium influx, an effect that may be due to the presence of different adenosine receptor sub-types (A1 or A2) in each of these two sub-groups. The identity of the adenosine-sensitive retinal neurons is currently being investigated.
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