ATP release in neuroepithelium of early embryonic retina

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Adenosine triphosphate (ATP) activates P2 purinoceptors. The activation of P2 purinoceptors induces CaィイD12+ィエD1 mobilization (release of CaィイD12+ィエD1from intracellular CaィイD12+ィエD1 stores) in the early embryonic chick neural retina during the period when the retinal cells have mitotic activities. After the CaィイD12+ィエD1 mobilization the entry of extracellular CaィイD12+ィエD1 (capacitative CaィイD12+ィエD1 entry) also occurs in the embryonic retina. To investigate the role of P2 purinoceptors and CaィイD12+ィエD1 mobilization in the regulation of retinal cell proliferation, the effects of the P2 purinoceptor antagonists and of the against ATP on DNA synthesis were studied in retinal organ cultures from embryonic day 3 (E3) chick. The antagonists inhibited [ィイD13ィエD1H]-thymidine incorporation in a dose-dependent manner and ATP enhanced [ィイD13ィエD1H]-thymidine incorporation to maximally 200% of control. The release of ATP was demonstrated in the medium of retinal organ cultures. The concentration of ATP increased 25-fold within one hour of incubation and this concentration was kept for at least 24 hours. These results indicated that P2 purinoceptors activated by autocrine or paracrine release of ATP were involved in the regulation of DNA synthesis in the neural retina at early embryonic stages. Then we studied the effects of an inhibitor of the CaィイD12+ィエD1 pump of intracelluar CaィイD12+ィエD1 stores and an inhibitor of capacitative CaィイD12+ィエD1 entry on the DNA synthesis in the retinal organ cultures from E3 chicks and in dissociated cultures from E7 and E9 chick retinae. It was demonstrated that both antagonists inhibited [ィイD13ィエD1H]-thymidine incorporation in a dose-dependent manner without affecting cell viability or morphology. These results suggested the involvement of CaィイD12+ィエD1 mobilization and capacitative CaィイD12+ィエD1 entry in the regulation of DNA synthesis in the developing neural retina.