Light conditions affect rhythmic expression of aquaporin 5 and anoctamin 1 in rat submandibular glands.

Circadian rhythms regulate various physiological functions and are, therefore, essential for health. Light helps regulate the master and peripheral clocks. The secretion rates of saliva and electrolytes follow a circadian rhythm as well. However, the relationship between the molecular mechanism of saliva water secretion and the peripheral circadian rhythm in salivary glands is not yet clear. The transmembrane proteins aquaporin5 () and anoctamin1 () are essential for water transport in the submandibular glands (SGs). The purpose of this study was to reveal the effect of light conditioning on the peripheral clock in SGs. We examined temporal expression patterns among clock genes, and , in rat SGs under light/dark (LD) and dark/dark (DD) conditions. We observed circadian rhythmic expression of , , , , and mRNAs under both LD and DD conditions. The expression levels of and peaked 6 h earlier under the DD condition than under the LD condition. Maintenance of the circadian rhythm of and expression even under the DD condition indicates that and may be controlled by clock genes; such genes are called clock-controlled genes (CCGs). Western blot analysis revealed the circadian oscillation and peak shift of AQP5 and ANO1expression under DD conditions. Clock genes may regulate the rhythmic expression of and and may control osmic gradients in SGs.