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Darlene A. Dartt, Robin R. Hodges; Interaction of α1D-Adrenergic and P2X7 Receptors in the Rat Lacrimal Gland and the Effect on Intracellular [Ca2+] and Protein Secretion. Invest. Ophthalmol. Vis. Sci. 2011;52(8):5720-5729. doi: 10.1167/iovs.11-7358.
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© ARVO (1962-2015); The Authors (2016-present)
To determine whether α1D-adrenergic receptors (α1D-AR) and P2X7 receptors interact by determining their effect on ATP release, intracellular [Ca2+] ([Ca2+]i), and protein secretion in rat lacrimal gland acini.
Exorbital lacrimal glands from male Sprague-Dawley rats were divided into pieces or digested with collagenase to form acini. With the use of an imaging system, [Ca2+]i was measured in acini loaded with fura-2. Adenosine triphosphate (ATP) release was determined using the luciferin-luciferase reaction. Peroxidase secretion, our index for protein secretion, was measured spectrophotometrically. Acini were stimulated with the P2X7 receptor agonist, (benzoylbenzoyl)adenosine 5′ triphosphate (BzATP) or the α1D-AR agonist phenylephrine with or without antagonist preincubation.
Phenylephrine increased ATP release from pieces in a time-dependent manner. The α1D-AR antagonist BMY7378 blocked the BzATP-stimulated increase in [Ca2+]i but not in peroxidase secretion. The P2X7 antagonist A438079 blocked the phenylephrine-stimulated increase in [Ca2+]i but not peroxidase secretion. The increase in [Ca2+]i caused by phenylephrine and BzATP used simultaneously or sequentially was additive, as was the increase in peroxidase secretion. The inhibition of protein kinase C isoforms or calcium calmodulin kinase II did not alter the BzATP-induced increase in [Ca2+]i.
The authors conclude that activation of α1D-AR releases ATP, which induces P2X7 receptors to increase [Ca2+]i but not to stimulate protein secretion. P2X7 receptors in turn activate α1D-AR to increase [Ca2+]i but not to stimulate protein secretion. Furthermore, α1D-AR compared with P2X7 receptors use different cellular mechanisms to increase [Ca2+]i and cause protein secretion.
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