title: Interaction of alpha1D-adrenergic and P2X(7) receptors in the rat lacrimal gland and the effect on intracellular [Ca2+] and protein secretion.
abstract: OBJECTIVE
  To determine whether α(1D)-adrenergic receptors (α(1D)-AR) and P2X(7) receptors interact by determining their effect on ATP release, intracellular [Ca(2+)] ([Ca(2+)](i)), and protein secretion in rat lacrimal gland acini.
  
  
  METHODS
  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, [Ca(2+)](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 P2X(7) receptor agonist, (benzoylbenzoyl)adenosine 5' triphosphate (BzATP) or the α(1D)-AR agonist phenylephrine with or without antagonist preincubation.
  
  
  RESULTS
  Phenylephrine increased ATP release from pieces in a time-dependent manner. The α(1D)-AR antagonist BMY7378 blocked the BzATP-stimulated increase in [Ca(2+)](i) but not in peroxidase secretion. The P2X(7) antagonist A438079 blocked the phenylephrine-stimulated increase in [Ca(2+)](i) but not peroxidase secretion. The increase in [Ca(2+)](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 [Ca(2+)](i).
  
  
  CONCLUSIONS
  The authors conclude that activation of α(1D)-AR releases ATP, which induces P2X(7) receptors to increase [Ca(2+)](i) but not to stimulate protein secretion. P2X(7) receptors in turn activate α(1D)-AR to increase [Ca(2+)](i) but not to stimulate protein secretion. Furthermore, α(1D)-AR compared with P2X(7) receptors use different cellular mechanisms to increase [Ca(2+)](i) and cause protein secretion.
authors.affiliation: Department of Ophthalmology, Schepens Eye Research Institute, Harvard Medical School, Boston, Massachusetts 02114, USA. darlene.dartt@schepens.harvard.edu
authors.forename: Darlene A
authors.initials: DA
authors.lastname: Dartt
authors.forename: Robin R
authors.initials: RR
authors.lastname: Hodges
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D058646:Adrenergic alpha-1 Receptor Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D066298:In Vitro Techniques; D007765:Lacrimal Apparatus / Q000378:metabolism*; D008297:Male; D010656:Phenylephrine / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism; D058911:Purinergic P2X Receptor Agonists / Q000494:pharmacology; D058920:Purinergic P2X Receptor Antagonists / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D020239:Receptor Cross-Talk / Q000187:drug effects / Q000502:physiology; D018340:Receptors, Adrenergic, alpha-1 / Q000378:metabolism*; D058486:Receptors, Purinergic P2X7 / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013666:Tears / Q000378:metabolism*; D013777:Tetrazoles / Q000494:pharmacology
chemical_list: C523668:3-(5-(2,3-dichlorophenyl)-1H-tetrazol-1-yl)methylpyridine; D058646:Adrenergic alpha-1 Receptor Agonists; D000317:Adrenergic alpha-Antagonists; D010879:Piperazines; D058911:Purinergic P2X Receptor Agonists; D058920:Purinergic P2X Receptor Antagonists; D011725:Pyridines; D018340:Receptors, Adrenergic, alpha-1; D058486:Receptors, Purinergic P2X7; D013777:Tetrazoles; D010656:Phenylephrine; C033901:3'-O-(4-benzoyl)benzoyladenosine 5'-triphosphate; D000255:Adenosine Triphosphate; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; C053428:BMY 7378; D002118:Calcium