title: Characterization of calcium signaling by purinergic receptor-channels expressed in excitable cells.
abstract: ATP-gated purinergic receptors (P2XRs) are a family of cation-permeable channels that conduct Ca(2+) and facilitate voltage-sensitive Ca(2+) entry in excitable cells. To study Ca(2+) signaling by P2XRs and its dependence on voltage-sensitive Ca(2+) influx, we expressed eight cloned P2XR subtypes individually in gonadotropin-releasing hormone-secreting neurons. In all cases, ATP evoked an inward current and a rise in [Ca(2+)](i). P2XR subtypes differed in the peak amplitude of [Ca(2+)](i) response independently of the level of receptor expression, with the following order: P2X(1)R < P2X(3)R < P2X(4)R < P2X(2b)R < P2X(2a)R < P2X(7)R. During prolonged agonist stimulation, Ca(2+) signals desensitized with different rates: P2X(3)R > P2X(1)R > P2X(2b)R > P2X(4)R >> P2X(2a)R >> P2X(7)R. The pattern of [Ca(2+)](i) response for each P2XR subtype was highly comparable with that of the depolarizing current, but the activation and desensitization rates were faster for the current than for [Ca(2+)](i). The P2X(1)R, P2X(3)R, and P2X(4)R-derived [Ca(2+)](i) signals were predominantly dependent on activation of voltage-sensitive Ca(2+) influx, both voltage-sensitive and -insensitive Ca(2+) entry pathways equally contributed to [Ca(2+)](i) responses in P2X(2a)R- and P2X(2b)R-expressing cells, and P2X(7)R operated as a nonselective pore capable of conducting larger amounts of Ca(2+) independently on the status of voltage-gated Ca(2+) channels. Thus, Ca(2+) signaling by homomeric P2XRs expressed in an excitable cell is subtype-specific, which provides an effective mechanism for generating variable [Ca(2+)](i) patterns in response to a common agonist.
authors.affiliation: Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: T A
authors.initials: TA
authors.lastname: Koshimizu
authors.forename: F
authors.initials: F
authors.lastname: Van Goor
authors.forename: M
authors.initials: M
authors.lastname: Tomić
authors.forename: A O
authors.initials: AO
authors.lastname: Wong
authors.forename: A
authors.initials: A
authors.lastname: Tanoue
authors.forename: G
authors.initials: G
authors.lastname: Tsujimoto
authors.forename: S S
authors.initials: SS
authors.lastname: Stojilkovic
mesh_terms: D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002478:Cells, Cultured; D011983:Receptors, Purinergic / Q000378:metabolism*; D018048:Receptors, Purinergic P2 / Q000378:metabolism; D058477:Receptors, Purinergic P2X3; D014162:Transfection
chemical_list: D015220:Calcium Channels; C546407:P2RX3 protein, human; D011983:Receptors, Purinergic; D018048:Receptors, Purinergic P2; D058477:Receptors, Purinergic P2X3; D002118:Calcium