title: Norepinephrine-induced calcium signaling and expression of adrenoceptors in avian tendon cells.
abstract: Sympathetic efferent nerves are present in tendons, but their function within tendon is unknown. alpha(1)-Adrenoceptors are expressed by a variety of cell types. In the presence of norepinephrine (NE), adrenoceptors activate G(q/11) signaling pathways that subsequently increase intracellular Ca(2+) concentration ([Ca(2+)](ic)). It was hypothesized that avian tendon cells express functional adrenoceptors that respond to NE by increasing [Ca(2+)](ic). Avian tendon cells were analyzed for mRNA expression of alpha(1)-adrenoceptors by RT-PCR. Avian tendons expressed the alpha(1A)- and alpha(1B)-adrenoceptor subtypes. Furthermore, both tendon surface epitenon cells and internal fibroblasts infused with a Ca(2+)-sensitive dye, fura 2, and stimulated with NE responded by increasing [Ca(2+)](ic). KMD-3213, an alpha(1A)-adrenoceptor antagonist, significantly reduced the Ca(2+) response. Other adrenoceptor antagonists had no effect on the Ca(2+) response. The absence of extracellular Ca(2+) also significantly reduced the response to NE, indicating that Ca(2+) influx contributed to the rise in [Ca(2+)](ic). This study provides the first evidence that tendon cells express adrenoceptors and that the NE-induced Ca(2+) response is coupled to the alpha(1A)-adrenoceptor subtype.
authors.affiliation: Department of Biomedical Engineering, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7055, USA.
authors.forename: Michelle E
authors.initials: ME
authors.lastname: Wall
authors.forename: James E
authors.initials: JE
authors.lastname: Faber
authors.forename: Xi
authors.initials: X
authors.lastname: Yang
authors.forename: Mari
authors.initials: M
authors.lastname: Tsuzaki
authors.forename: Albert J
authors.initials: AJ
authors.lastname: Banes
mesh_terms: D018674:Adrenergic Antagonists / Q000494:pharmacology; D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D002645:Chickens; D003238:Connective Tissue / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism; D009638:Norepinephrine / Q000494:pharmacology*; D012333:RNA, Messenger / Q000032:analysis; D011941:Receptors, Adrenergic / Q000096:biosynthesis* / Q000187:drug effects; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013710:Tendons / Q000166:cytology / Q000294:innervation* / Q000378:metabolism*
chemical_list: D018674:Adrenergic Antagonists; D012333:RNA, Messenger; D011941:Receptors, Adrenergic; D009638:Norepinephrine