Molecular identification and localization of P2X receptors in the rat lens

There is growing evidence suggesting that purine-mediated signaling pathways play important roles in the ocular lens. We have previously reported the expression of P2Y receptors in the lens; and in this present study, we show that P2X receptors are also expressed. Transcripts for P2X1-7 receptors were detected in lens fiber cells using the reverse-transcription polymerase chain reaction (RT-PCR). Western blot analysis confirmed the expression of all P2X receptor subtypes at the protein level. Immunohistochemistry revealed P2X1 and P2X7 expression in the cytoplasm of cortical fiber cells. P2X2 expression was confined to the apical-apical interface between epithelial and fiber cells with little expression in cortical fiber cells. In contrast, P2X3, P2X4, P2X5 and P2X6 were expressed throughout the lens extending from the outer cortex through to the core. In the outer cortex, immunolocalisation of these P2X receptors was predominantly cytoplasmic. However, deeper into the lens, P2X receptor immunolabeling became more membranous, indicating the recruitment of P2X receptors from cytoplasmic vesicles into the membranes of mature fiber cells in the lens core. Western blotting confirmed regional differences in P2X receptor expression. The differential expression of P2X receptors in the ocular lens indicates that the purinergic signaling pathways may be involved in the maintenance of lens homeostasis.