title: Xestospongin B, a competitive inhibitor of IP3-mediated Ca2+ signalling in cultured rat myotubes, isolated myonuclei, and neuroblastoma (NG108-15) cells.
abstract: Xestospongin B, a macrocyclic bis-1-oxaquinolizidine alkaloid extracted from the marine sponge Xestospongia exigua, was highly purified and tested for its ability to block inositol 1,4,5-trisphosphate (IP(3))-induced Ca(2+) release. In a concentration-dependent manner xestospongin B displaced [(3)H]IP(3) from both rat cerebellar membranes and rat skeletal myotube homogenates with an EC(50) of 44.6 +/- 1.1 microM and 27.4 +/- 1.1 microM, respectively. Xestospongin B, depending on the dose, suppressed bradykinin-induced Ca(2+) signals in neuroblastoma (NG108-15) cells, and also selectively blocked the slow intracellular Ca(2+) signal induced by membrane depolarization with high external K(+) (47 mM) in rat skeletal myotubes. This slow Ca(2+) signal is unrelated to muscle contraction, and involves IP(3) receptors. In highly purified isolated nuclei from rat skeletal myotubes, Xestospongin B reduced, or suppressed IP(3)-induced Ca(2+) oscillations with an EC(50) = 18.9 +/- 1.35 microM. In rat myotubes exposed to a Ca(2+)-free medium, Xestospongin B neither depleted sarcoplasmic reticulum Ca(2+) stores, nor modified thapsigargin action and did not affect capacitative Ca(2+) entry after thapsigargin-induced depletion of Ca(2+) stores. Ca(2+)-ATPase activity measured in skeletal myotube homogenates remained unaffected by Xestospongin B. It is concluded that xestospongin B is an effective cell-permeant, competitive inhibitor of IP(3) receptors in cultured rat myotubes, isolated myonuclei, and neuroblastoma (NG108-15) cells.
authors.affiliation: Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, casilla 70005, Santiago 7, Chile.
authors.forename: Enrique
authors.initials: E
authors.lastname: Jaimovich
authors.forename: César
authors.initials: C
authors.lastname: Mattei
authors.forename: José Luis
authors.initials: JL
authors.lastname: Liberona
authors.forename: Cesar
authors.initials: C
authors.lastname: Cardenas
authors.forename: Manuel
authors.initials: M
authors.lastname: Estrada
authors.forename: Julien
authors.initials: J
authors.lastname: Barbier
authors.forename: Cécile
authors.initials: C
authors.lastname: Debitus
authors.forename: Dominique
authors.initials: D
authors.lastname: Laurent
authors.forename: Jordi
authors.initials: J
authors.lastname: Molgó
mesh_terms: D000470:Alkaloids / Q000494:pharmacology*; D000818:Animals; D001667:Binding, Competitive; D020013:Calcium Signaling / Q000187:drug effects*; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D047028:Macrocyclic Compounds; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D009447:Neuroblastoma / Q000378:metabolism* / Q000473:pathology; D010080:Oxazoles; D051381:Rats
chemical_list: D000470:Alkaloids; D047028:Macrocyclic Compounds; D010080:Oxazoles; D015544:Inositol 1,4,5-Trisphosphate; C078549:xestospongin B