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Chuanqing Ding, Michael Lu, Jianyan Huang; ENaC in the rabbit lacrimal gland and its changes during Sjögren’s syndrome and pregnancy. Invest. Ophthalmol. Vis. Sci. 2013;54(15):916.
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The epithelial sodium channel (ENaC), which is comprised of α, β, and γ subunits, plays a critical role in the control of Na+ balance and has been implicated in the development and progression of exocrine gland pathology. The aim of the present study was to investigate the expression of ENaC in the rabbit lacrimal gland (LG) and its potential changes in rabbits with induced autoimmune dacryoadenitis (IAD), a rabbit model of Sjögren’s syndrome, and in term-pregnant rabbits, a physiological condition that has been shown to exhibit altered LG secretion and ocular surface symptoms.
Total mRNA of α, β, and γ subunits was extracted from whole LG, acinar cells, and epithelial cells from various duct segments by laser capture microdissection (LCM) for real time RT-PCR. LG lysates were processed for Western blot and cryosections of LG were used for immunofluorescence. Goat polyclonal primary antibodies of α, β, and γ were purchased from Santa Cruz Biotechnology (Santa Cruz, CA).
mRNA for both α and γ was expressed in whole LG lysates while β was undetectable. In rabbits with IAD, the levels of mRNA for α and γ were 20.9% and 58.9% lower (p<0.05) while no significant changes were observed in term-pregnant rabbits (p>0.05). However, we were unable to detect mRNA of any of these three subunits in LCM samples of epithelial cells due to their extremely low level. Western blot demonstrated bands for both α (90 kDa) and γ (85 kDa) but β was undetectable. In rabbits with IAD, densitometry analysis showed that expression of α decreased 22% while γ decreased 26% (p<0.05). In pregnant rabbits, however, α expression was 31% lower while γ was 34% lower (p<0.05). From immunofluorescence studies, all subunits were present in ductal cells only with virtually no immunoreactivity detected in acini. No noticeable changes of their distribution pattern and intensity were found in rabbits with IAD or pregnant rabbits.
The present data demonstrated the presence of ENaC in the rabbit LG and its changes in rabbits with IAD and pregnant rabbits. This suggests that ENaC may contribute to the pathogenesis of altered LG secretion and ocular surface symptoms in these animals. The exact mechanisms of how ENaC functions in the LG under physiological and pathological conditions certainly warrant further investigations.
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