Molecular and functional mapping of regional differences in P2Y receptor expression in the rat lens

Extracellular ATP has been shown to mobilize intracellular Ca2+ in cultured ovine lens epithelial cells and in human lens epithelium, suggesting a role for purines in the modulation of lens transparency. In this study, we characterized the expression profiles of P2Y receptor isoforms throughout the rat lens at both the molecular and the functional levels. RT-PCR indicated that P2Y1, P2Y2, P2Y4 and P2Y6 are expressed in the lens, while P2Y12, P2Y13 and P2Y14 are not. Immunohistochemistry, using isoform specific antibodies, indicated that the epithelium does not express P2Y1 and P2Y2, but that the underlying fiber cells, which differentiate from the epithelial cells, exhibit strong membranous labeling. Although co-expressed in fiber cells, differences in P2Y1 and P2Y2 expression were apparent. P2Y1 expression extended deeper into the lens than P2Y2, and its expression co-localized with Cx50 gap junction plaques, while P2Y2 did not. Labeling for P2Y4 and P2Y6 receptors were observed in both epithelial cells and fiber cells, but the labeling was predominantly cytoplasmic in nature. While purine agonist (ATP, ADP, UTP and UDP) application to the lens induced mobilization of intracellular Ca2+ in cortical fiber cells, little to no effect was observed in the anterior and equatorial epithelium. Thus the inability of UTP and UDP to mobilize intracellular Ca2+ in the epithelium and the predominately cytoplasmic location of P2Y4 and P2Y6 suggests that these receptors may represent an inactive pool of receptors that may be activated under non-physiological conditions. In contrast, our results indicated that P2Y1 and P2Y2 are functionally active in fiber cells and their differential subcellular expression patterns suggest they may regulate distinct processes in the lens under steady state conditions.