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J. Gierow, S. K. Carlsson, D. Delbro, M. C. Edman; Adenosine Receptors, cAMP and Secretion in Rabbit Lacrimal Gland Acinar Cells. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1912.
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We have previously reported of the presence of two adenosine receptors, A1 and A2a, in the rabbit lacrimal gland (Invest. Opthalmol. Vis. Sci. 47, E-abstract 1943, 2006). Stimulation of the receptors, in both cases, resulted in an attenuation of carbachol stimulated secretion. Since the receptors, in most systems, have been described to have different effects on adenylyl cyclase, it was of interest to study the role of cAMP in adenosine evoked intracellular signalling.
Rabbit lacrimal gland acinar cells for secretion studies were prepared according to our standard procedure (Andersson et al., Exp. Eye Res. 83, 543-553, 2006) yielding single cells that were placed in a serum-free culture medium on standard culture plates for two days, thus allowing the cells to re-organized into acinar-like structures. The cultured cells were rinsed briefly, pre-incubated, and then incubated w./w.o. secretagogues and/or inhibitors as indicated. Secretion was determined enzymatically as secreted beta-hexosaminidase activity, and cAMP formed was measured using a cAMP assay kit (R & D Systems).
A 2-fold increase of beta-hexosaminidase secretion was observed when cells were stimulated by adenosine, CPA (A1 agonist) and CPCA (A2a agonist). Combination of either one with carbachol, resulted in an approximate 10-fold, synergistic increase of secretion over basal. cAMP production was increased 2-4-fold by purinergic stimulation, but no significant additional changes were detected by combinations with carbachol, except for combinations with adenosine which resulted in an additional 2-fold increase.
Our results indicate that stimulation of secretion through A1- and A2a-receptors act by increases of cAMP in the rabbit lacrimal gland. However, the synergistic effect on secretion observed by combinations with carbachol does not appear to be paralleled by a similar increase in cAMP formation, except for adenosine which evokes a potentiation, perhaps by acting partly through yet another receptor.
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