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T. Puthussery, P. Yee, A.J. Vingrys, E.L. Fletcher; Modulation of photoreceptor function by P2X6 and P2X7 purinoceptors. . Invest. Ophthalmol. Vis. Sci. 2004;45(13):5363.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: There is accumulating evidence for the involvement of purinergic receptors in neurotransmission and neuromodulation in the mammalian retina. However, functional studies have been limited to glial cell responses. The aim of this study was to explore the neuronal localization of the P2X6 and P2X7 receptor subunits in the outer retina and to explore their function using the electroretinogram. Methods:For immunocytochemistry, adult Sprague Dawley rats were deeply anaesthetised (ketamine:xylazine 60:5mg/kg i.m.) and sacrificed by anaesthetic overdose (sodium pentobarbital; 60mg/kg i.p.). Retinae were processed for immunofluorescence immunocytochemistry and pre and postembedding immunoelectron microscopy. Sections were immunolabelled with an anti–P2X7 antibody (Chemicon) and anti–P2X6 antibody (Sigma). Dark adapted electroretinograms were collected from anaesthetized animals (ketamine:xylazine 60:5mg/kg i.m.) using a saturating twin flash paradigm to isolate the rod contributions (10kHz, 2log.cd.m–2). Following baseline recordings, animals were administered with a sham intravitreal injection of PBS (n=5) or a treatment injection of 10mM BzATP (n=4), a P2X7 receptor selective agonist. Signals were collected at 3 min post injection and then at 2 min intervals for 45 min. Photoreceptoral contributions (PIII) were modelled according to the characteristics of the phototransduction cascade and the post receptoral (PII) extracted. Results:P2X7 receptors were observed at the photoreceptor ribbon and on horizontal cell processes within and below the photoreceptor triad. P2X6 receptors were localised to the photoreceptor synaptic terminal. Following intravitreal injection with 10mM BzATP, a 50% increase in the rod PIII amplitude was observed peaking at 30 min post injection. The rod PII showed a 40% reduction in amplitude which occurred at 15 min postinjection and showed a gradual recovery to baseline by 30 min post injection. Conclusions:This study demonstrates that P2X receptors are expressed on multiple neuronal classes in the OPL. In addition, we demonstrate that intravitreal administration of a P2X7 receptor specific agonist has a marked effect on both photoreceptoral and postreceptoral retinal functions. This data adds to the complexity of retinal signalling within the outer retina.
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