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A.H. Kihara, A.S. Moriscot, D.E. Hamassaki-Britto; Modulation of Connexins Gene Expression in the Mouse Retina by Dark Adaptation . Invest. Ophthalmol. Vis. Sci. 2003;44(13):5155.
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Purpose:The channels formed by connexins (Cx) and grouped as gap junctions provide metabolic and electrical coupling, allowing the passage of small molecules such as second messengers and ions, which in excitable cells provide cell communication by means of eletrotonic potential. In retina, conductance of these channels is decreased by neuromodulators, such as nitric oxide and dopamine, which in turn are related with ambient light levels. Although these neuromodulators are known to uncouple cells, their effects on connexin gene expression are still poorly understood. Our aim in the present study was to determine whether gene expression of specific connexins (Cx26, Cx32, Cx43, Cx45 and Cx50) is modulated by dark adaptation in the mouse retina. Methods:24 adult mice were divided into 3 groups (Control, 1 day and 7 days dark-adapted), sacrificed with an overdose of ketamine and xylazine, and their retinas were dissected for RNA isolation by using TRIzol. mRNA was reversed transcribed and cDNA was amplified with a 5700 SDS Real-Time PCR machine by using specific primers for different connexins. cDNAs abundance for GAPDH and ribosomal 18S were also determined as internal controls. Data were entered into a multivariate analysis of variance (MANOVA), followed by pairwise comparisons (Tukey's HSD test). Results: Cx43 showed a significant decrease (P=0.02) after 7 days of dark adaptation, while Cx45 gene expression decreased significantly as early as 1 day after dark adaptation (P=0.05). Additionally, we have noted that 18S gene expression varied with dark adaptation, while GAPDH expression levels showed no significant differences in all groups tested. Cx26, Cx32 and Cx50 showed no significant modulation. Conclusions: Dark adaptation downregulates the expression of Cx43 and Cx45 in the mouse retina. Differences in connexins distribution might account for this result, since there are evidences showing that Cx43 is expressed by glial cells, whereas Cx45 is present in neurons (Güldenagel et al., J. Comp. Neurol., 2000). Probably the differential modulation of connexins reflects their distinct physiological role in dark adaptation process.
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