Involvement of P2 purinoceptors in the regulation ofdna synthesis in the neural retina of chick embryo

Abstract

The activation of P2 purinoceptors induces Ca2+ mobilization in the early embryonic chick neural retina. This purinergic Ca2+ response declines parallel with the decrease in mitotic activity during retinal development. To investigate the role of P2 purinoceptors in the regulation of retinal cell proliferation, we studied the effects of the P2 purinoceptor antagonists suramin and pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS), and of the agonist ATP on DNA synthesis in retinal organ cultures from embryonic day 3 (E3) chick. Suramin inhibited [3H]-thymidine incorporation in a dose-dependent manner (IC50: approximately 70 microM). PPADS also reduced [3H]-thymidine incorporation with maximum inhibition of 46% at 100 microM. Exogenous ATP enhanced [3H]-thymidine incorporation in a dose-dependent manner to maximally 200% of control (EC50: approximately 70 microM). In dissociated retinal cultures from E7 chick, both antagonists showed similar inhibitory effects on [3H]-thymidine incorporation without affecting cell viability. In line with these observations, the presence of extracellular ATP was demonstrated both in vitro and in vivo. In the medium of E3 retinal organ cultures, the concentration of ATP increased 25-fold within 1 h of incubation and this concentration was kept for at least 24 h. In the chick amniotic fluid, the ATP concentration was nearly 3 microM at E3 and declined to 0.15 microM at E7. The results indicate that P2 purinoceptors activated by autocrine or paracrine release of ATP are involved in the regulation of DNA synthesis in the neural retina at early embryonic stages.

Zebrafish mutations ingartandpaicsidentify crucial roles for de novo purine synthesis in vertebrate pigmentation and ocular development

“…With regard to retinoblast proliferation and cell cycle progression, it has been demonstrated that ATP, released from the RPE, can nonautonomously modulate the rate of the retinoblast cell cycle and thereby regulate overall rates of eye growth (Martins and Pearson, 2008;Pearson et al, 2002;Pearson et al, 2005). Using chicken retinal explants and pharmacological manipulations, ATP was shown to mechanistically act by modulating the rate of mitosis (Pearson et al, 2002) and/or the rate of DNA synthesis (Sugioka et al, 1999;Pearson et al, 2005). Given the key enzymatic roles that the proteins encoded by the gart, paics and adss loci play in the biosynthesis of ATP, the most parsimonious explanation for the cellular mechanism underlying the microphthalmia observed in gart, paics and adss zebrafish mutants and/or morphants is that, in the absence of sufficient ATP, DNA synthesis during S phase is delayed.…”

Activation of P2Y receptors stimulates potassium and cation currents in acutely isolated human Müller (glial) cells

“…In the retina, ATP has been suggested to act as a signaling molecule (Perez et al, 1988) being involved in early retinal development (Sugioka et al, 1999) and in neuronal information processing of the mature retina (Neal and Cunningham, 1994). Therefore, extracellularly released ATP may be involved in neuron-to-glia signaling in the retina.…”

Characterization and expression of ATP P2X4 receptor from embryonic chick skeletal muscle

“…The physiological function of cP2X 4 receptors in embryonic skeletal muscle remains to be elucidated. In embryonic chick neural retina, ATP receptor was reported to regulate the synthesis of DNA [Sugioka et al, 1999]. It is not clear whether P2X4 receptor is involved in such a process, although cP2X 4 RNA is highly expressed in embryonic chick retina.…”