Abstract
Purpose: :
Many of the cell types in the retina generate sodium currents. The sodium channel isoforms underlying these currents have not been completely characterized. In this study, we applied qPCR and immunolocalization to determine the expression patterns of sodium channel isoforms in rat retina.
Methods: :
In Sprague Dawley rats, we measured retinal sodium channel gene expression at four ages p7, p15, p30 and at 3-4 months using qPCR. Amplicons from the qPCR reaction product were annealed to pGEM-T vectors, amplified and sequenced for confirmation of the target sodium channel sequences. Using isoform-specific antibodies, we examined channel protein localization with confocal microscopy.
Results: :
The mRNA for NaV1.1, NaV1.2, and NaV1.6 was strongly expressed throughout development. Expression of NaV1.3 mRNA decreased 3-fold from p7 to p15, but then remained stable to the age of four months. We demonstrated a low level of expression of NaV1.8 and NaV1.9 mRNA and greater expression of NaV1.7, three genes normally considered to be expressed only in the PNS. Using confocal microscopy, we found substantial immunoreactivity of the Nav1.7, 1.8, and 1.9 isoforms in the retina. Nav1.7 and 1.9 appear to be localized to photoreceptors and to synaptic structures in the outer plexiform layer, while Nav1.8 is expressed in a subset of retinal ganglion cells and their processes.
Conclusions: :
A diverse set of sodium channel isoforms are expressed in the mammalian retina with different pattern of cellular localization for each suggesting unique contributions to signal processing and integration in the complex neuronal network of the retina.
Keywords: ion channels • retina • microscopy: light/fluorescence/immunohistochemistry