Role Of Muscarinic Acetylcholine Receptors And Ca2+ Signaling In Tear Secretion

Abstract

Purpose: : Muscarinic acetylcholine receptor (mAchR) is a G-coupled receptor which consists of 5 distinct subtypes. However, relationship between tear secretion and subtypes of mAchR has not been reported. Therefore, we examined the role of mAchRs and Ca2+ signaling in tear secretion by using various mAchR genes knockout (mAchRKO) mice.

Methods: : Tear secretion was measured after treatment with 3 mg/kg pilocarpine. Pathological analyses were performed to evaluate lacrimal gland tissue sections with a light microscopy and an electron microscopy. In order to examine Ca2+ signaling induced by cholinergic stimulation in lacrimal gland, the Ca2+ in lacrimal gland acinar cells from mAchRKO mice and wild-type mice were measured ratiometrically using Ca2+-sensing dye (Fura-2).

Results: : Double deficient mice of M1 and M3 (M1/M3 AchRKO) genes showed significant decrease in pilocarpine-stimulated tear secretion compared with wild type mice. In addition, tear deficiency in M1/M3 AchRKO mice was caused by severely impaired Ca2+ signaling in the lacrimal gland acinar cells. Lacrimal gland dysfunction caused abnormal accumulation of secretory granules in the acinar epithelia.

Conclusions: : We concluded that M1/M3 AchRs and Ca2+ signaling are key molecules for tear secretion. Our findings suggest that M1/M3 AchR KO mice may become a novel dry eye model.

Keywords: lacrimal gland • cornea: tears/tear film/dry eye • acetylcholine