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R. R. Hodges, D. A. Dartt; Interaction of 1D-Adrenergic and Muscarinic Receptors With P2X7 Receptors in Rat Lacrimal Gland Acini. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4164.
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We previously showed that α1D-adrenergic, cholinergic, and P2X7 receptor agonists increased intracellular calcium ([Ca2+]i) in rat lacrimal gland acini. In this study, we determined if α1D-adrenergic and cholinergic agonists interact with P2X7 receptors and the effect of the interaction on [Ca2+]i.
Rat lacrimal glands were removed from male Sprague Dawley rats and acini isolated by collagenase digestion. [Ca2+]i was measured using InCyte Im2TM Ratio Imaging System in acini incubated with the calcium indicator dye fura2 in response to the α1D -adrenergic agonist phenylephrine (Ph) or the cholinergic agonist carbachol (Cch). In some experiments A43871 (10-5 M), an inhibitor of the P2X7 receptors, was added 1 h prior to stimulation while in other experiments apyrase (20 U), an ATPase diphosphohydrolase that catalyzes the hydrolysis of ATP to ADP, was added immediately prior to agonist addition.
Ph (10-8-10-3 M) increased [Ca2+]i in a concentration dependent manner with a maximum of 149 ± 16 nM at 10-5 M. Cch (10-8-10-3 M) also increased [Ca2+]i in a concentration dependent manner with a maximum of 371 ± 114 nM at 10-5 M. Addition of A43871 significantly decreased Ph-stimulated increase in peak [Ca2+]i by 52 ± 14% from 161 ± 39 nM to 81 ± 34 nM. Apyrase also significantly decreased Ph-stimulated increase in peak [Ca2+]i by 75 ± 19 % to 42 ± 38 nM. In contrast, neither A43871 nor apyrase had any significant effect on Cch-stimulated increase in peak [Ca2+]i.
We conclude that α1D-adrenergic and P2X7 receptors interact in the lacrimal gland while muscarinic receptors do not interact with P2X7 receptors.
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