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

Abstract

The study reveals the presence of the adenosine A(2) receptor subtypes as well as a role for them in lacrimal gland secretion, and especially in the synergy with purinergic and cholinergic stimulation.

Signaling Pathways of Purinergic Receptors and Their Interactions with Cholinergic and Adrenergic Pathways in the Lacrimal Gland

“…A 1 , A 2A , and A 2B receptors have been identified in the LGs of rabbits by reverse transcription polymerase chain reaction (RT-PCR) and immunofluorescence microscopy. 23,25 The intracellular locations of A 1 receptors differed slightly from the localization of the A 2A and A 2B . A 1 was expressed almost exclusively in the basolateral membranes of acini, while A 2A and A 2B were found not only in the basolateral membrane but also in the cytosol.…”

“…37 Similar to A 1 agonists, the A 2 agonist 5¢-(N-cyclopropyl)carboxamidoadenosine (CPCA) alone caused a small increase in protein secretion from rabbit LG acini. 23 When added with carbachol, a potentiation of secretion also occurred. Using antagonists to A 2A and A 2B receptors, only the A 2B antagonist blocked the potentiation.…”

“…In addition to neural stimulation, protein secretion from acinar cells can also be stimulated by ATP and its metabolites. 21,[23][24][25][26][27] ATP is released along with the neurotransmitters Ach and norepinephrine 28 and can also be released from cells by mechanical stimulation. 29 ATP can then act in an autocrine manner (acting on the same cell) or paracrine manner (acting on neighboring cell).…”

“…The A 2B antagonist also blocked the potentiation of secretion with carbachol and adenosine. 23 However, nature of the interactions between the 2 pathways was not investigated. A 2 receptors have been shown to stimulate AC to increase cAMP.…”

p38 Mitogen-activated protein kinase modulates exocrine secretion in rabbit lacrimal gland

“…Immunofluorescence Immunofluorescence methodology used was described elsewhere [10]. In brief, isolated LGs were fixed and sectioned into 5 µm sections.…”