Adenosine A₂ Receptor Presence and Synergy with Cholinergic Stimulation in Rabbit Lacrimal Gland

Abstract

Purpose: Secretion from the lacrimal gland is an important part of the well-being of the eye, and a central part in the search for treatment of dry eye syndrome. Adenosine has stimulatory effects on the lacrimal gland, and can potentiate the effect of the cholinergic agonist carbachol (Cch). The aim of the present study is to investigate the presence of the adenosine A₂ receptor subtypes A_2A and A_2B in the rabbit lacrimal gland, and to characterize their role in regulated acinar cell secretion.

Methods: Expression of the receptors was investigated using reverse transcriptase-PCR (RT-PCR) and immunofluorescence, and secretion effects were studied using a secretion assay in isolated lacrimal gland acinar cells.

Results: Presence of both receptors was detected by RT-PCR and immunofluorescence. The secretion assay revealed a minor effect of stimulation of the A₂ receptors, and a strong synergistic effect with the cholinergic agonist Cch. The synergistic effect was significantly reduced by the A_2B antagonist PSB 1115, but not by the A_2A antagonist SCH 58261, indicating that A_2B is the receptor responsible for this potentiation.

Conclusions: The study reveals the presence of the adenosine A₂ receptor subtypes as well as a role for them in lacrimal gland secretion, and especially in the synergy with purinergic and cholinergic stimulation.

KEYWORDS::

• Acetylcholine
• Adenosine receptors
• Lacrimal gland
• Purinergic receptors
• Tear secretion

ACKNOWLEDGMENTS

The study was funded by Crown Princess Margareta’s Eye Research Foundation (J.P.G.), the Swedish Knowledge Foundation (J.P.G.) and the University of Kalmar Faculty Research Grant (J.P.G., D.D.).

Declaration of interest: The authors report no conflict of interest. The authors alone are responsible for the content and writing of the paper.