title: Multiple receptor activation elicits synergistic IP formation in nonpigmented ciliary body epithelial cells.
abstract: We have examined the interaction between muscarinic and alpha(2)-adrenergic receptor activation on inositol phosphate (IP) formation in the nonpigmented cells of the ciliary body epithelium (NPE cells) of the rabbit. We have compared these changes with those previously observed in the intracellular free Ca(2+) concentration. Whereas muscarinic receptor activation causes an increase in intracellular Ca(2+) and IP formation, activation of alpha(2)-receptors does not significantly increase either intracellular Ca(2+) or IPs over basal levels. However, simultaneous activation of muscarinic and alpha(2)-adrenergic receptors with the specific agonists carbachol and UK-14304 produces massive Ca(2+) increases and results in a synergistic increase in IP formation. This synergistic IP formation is inhibited by both muscarinic and alpha(2)-adrenergic receptor antagonists as well as by pertussis toxin and an inhibitor of phospholipase C. IP formation is predominantly independent of intracellular Ca(2+), because it is decreased but not prevented by blocking the entry of Ca(2+) with LaCl(3) or chelating intracellular Ca(2+) with 1, 2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid. Thus synergistic IP formation underlies, at least in part, the synergistic increase in intracellular Ca(2+) resulting from simultaneous activation of muscarinic and alpha(2)-adrenergic receptors.
authors.affiliation: Department of Physiological Science, University of California, Los Angeles, California 90095, USA. mariannc@physci.ucla.edu
authors.forename: M C
authors.initials: MC
authors.lastname: Cilluffo
authors.forename: E
authors.initials: E
authors.lastname: Esqueda
authors.forename: N A
authors.initials: NA
authors.lastname: Farahbakhsh
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D000068438:Brimonidine Tartrate; D002118:Calcium / Q000502:physiology; D002217:Carbachol / Q000494:pharmacology; D002478:Cells, Cultured; D002924:Ciliary Body / Q000166:cytology / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism; D007295:Inositol Phosphates / Q000096:biosynthesis*; D018721:Muscarinic Agonists / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D011817:Rabbits; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D007295:Inositol Phosphates; D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D011810:Quinoxalines; D011942:Receptors, Adrenergic, alpha; D011976:Receptors, Muscarinic; D000068438:Brimonidine Tartrate; D002217:Carbachol; D002118:Calcium