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H. Suzuki, R. Hu, J. C. Lim, P. J. Donaldson; Diverse and Dynamic Expression of ATP Receptors in the Rat Ocular Lens. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1898.
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Functional studies have suggested that extracellular nucleotide signaling takes place in the ocular lens and may regulate connexin gap-junctions that are critical for the lens homeostasis 1, 2. This study aims to further extend our knowledge of such receptor-mediated signaling in the lens by characterizing the expression of extracellular nucleotide receptors (P2X and P2Y) in the rat lens.
RT-PCR was utilized to study the expression of P2X1-7 and P2Y1,2,4,6,12-14 at the transcript level. Immunohistochemistry was applied to characterize their localization patterns on fixed lens sections. In addition, lenses were incubated in artificial aqueous humor (AAH) prior to fixation to monitor the change in the protein expression after culturing of the lens.
P2X1-7 and P2Y1-2,4,6 were expressed at the transcript level, while P2Y12-14 were absent. By immunohistochemistry, P2Y1 and P2Y2 were localized on the broad sides of the fiber cell membrane and were absent in epithelial cells. Furthermore, P2Y1 was co-localized closely with Connexin 50 gap-junction plaques while similar pattern was not observed for P2Y2. P2X2 exhibited an unique expression that the strongest labeling was observed at the epithelial-fiber cell interface. P2Y4,6 and P2X1,7 were expressed in both epithelial and cortical fiber cells, where they were found to be predominantly cytoplasmic. P2X3-6 were expressed in similar pattern as P2X1,7 in the outer cortex of the lens, however P2X3-6 were also identified in the lens core where they appeared to be present in the fiber cell membrane, suggesting that differentiation-dependent membrane insertion of these receptors take place. Furthermore, upon culturing of the lens in AAH, modulations to the expression patterns of P2X and P2Y were observed in both epithelial and fiber cells, highlighting the dynamic nature of the receptor expression in the lens.
Taken together, the rat lens expresses a broad range of both P2Y and P2X receptors. Their differential and dynamic expression in the lens may reflect their diverse functions under physiological and/or pathophysiological conditions.1. Collison, D. J. & Duncan, G. Regional Differences in Functional Receptor Distribution and Calcium Mobilization in the Intact Human Lens. Investigative Ophthalmology & Visual Science 42, 2355-2363 (2001).2. Churchill, G. C., Lurts, M. M. & Louis, C. F. Ca2+ regulation of gap junctional coupling in lens epithelial cells. American Journal of Physiology Cell Physiology 281, C972-C981 (2001).
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