Adenosine A2Receptor Presence and Synergy with Cholinergic Stimulation in Rabbit Lacrimal Gland

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 A2A and A2B 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 A2B antagonist PSB 1115, but not by the A2A antagonist SCH 58261, indicating that A2B 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.