title: Store-refilling involves both L-type calcium channels and reverse-mode sodium-calcium exchange in airway smooth muscle.
abstract: The aim of the present study was to examine the relative contributions to store-refilling of the two following voltage-regulated calcium ion influx pathways: 1) L-type-Ca(2+) channels; and 2) the reverse-mode of the sodium-calcium exchanger (NCX). Successive acetylcholine-induced contractions, triggered in bovine tracheal smooth muscle strips, were measured to determine the effect of intervention on contractions as an indication of the extent of store-refilling. Pre-treating the tissues with cromakalim significantly reduced the magnitude of successive contractions. Zero-Ca(2+) bathing media abolished the contractions, an effect that was completely reversed upon reintroduction of Ca(2+). Inhibition of L-type Ca(2+) channels, with nifedipine, significantly reduced the magnitude of the contractions. Similarly, inhibition of the reverse-mode of the NCX, with KB-R7943, significantly reduced the magnitude of the contractions. However, neither nifedipine nor KB-R7943 alone reduced contractions to the same extent as observed under zero-Ca(2+) conditions. Concurrent treatment with nifedipine and KB-R7943 almost abolished successive contractions. Furthermore, concurrent treatment with nifedipine and zero-Na(+) bathing media displayed a significantly greater effect than nifedipine alone. Probing the expression of NCX1 isoforms by Western blotting revealed the presence of three bands of 160, 120 and 110 kDa. The 120- and 110-kDa bands were identified as variably spliced NCX isoforms, NCX1.1 and NCX1.3, respectively. Taken together, these data suggest that influx of calcium ions through both L-type calcium channels and the reverse-mode of the sodium-calcium exchanger is necessary for complete store-refilling in airway smooth muscle.
authors.affiliation: Firestone Institute for Respiratory Health, St. Joseph's Healthcare and Department of Medicine, McMaster University, Hamilton, ON, Canada L8N 4A6.
authors.forename: S
authors.initials: S
authors.lastname: Hirota
authors.forename: L J
authors.initials: LJ
authors.lastname: Janssen
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D015153:Blotting, Western; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D002417:Cattle; D019806:Cromakalim / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D019831:Sodium-Calcium Exchanger / Q000378:metabolism*; D013890:Thiourea / Q000031:analogs & derivatives / Q000494:pharmacology; D014132:Trachea / Q000378:metabolism*
chemical_list: C101670:2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate; D020746:Calcium Channels, L-Type; D019831:Sodium-Calcium Exchanger; D019806:Cromakalim; D013890:Thiourea; D009543:Nifedipine; D000109:Acetylcholine