title: Redox-sensitive stimulation of type-1 ryanodine receptors by the scorpion toxin maurocalcine.
abstract: The scorpion toxin maurocalcine acts as a high affinity agonist of the type-1 ryanodine receptor expressed in skeletal muscle. Here, we investigated the effects of the reducing agent dithiothreitol or the oxidizing reagent thimerosal on type-1 ryanodine receptor stimulation by maurocalcine. Maurocalcine addition to sarcoplasmic reticulum vesicles actively loaded with calcium elicited Ca²⁺ release from native vesicles and from vesicles pre-incubated with dithiothreitol; thimerosal addition to native vesicles after Ca²⁺ uptake completion prevented this response. Maurocalcine enhanced equilibrium [³H]-ryanodine binding to native and to dithiothreitol-treated reticulum vesicles, and increased 5-fold the apparent Ki for Mg²⁺ inhibition of [³H]-ryanodine binding to native vesicles. Single calcium release channels incorporated in planar lipid bilayers displayed a long-lived open sub-conductance state after maurocalcine addition. The fractional time spent in this sub-conductance state decreased when lowering cytoplasmic [Ca²⁺] from 10 μM to 0.1 μM or at cytoplasmic [Mg²⁺]≥30 μM. At 0.1 μM [Ca²⁺], only channels that displayed poor activation by Ca²⁺ were readily activated by 5 nM maurocalcine; subsequent incubation with thimerosal abolished the sub-conductance state induced by maurocalcine. We interpret these results as an indication that maurocalcine acts as a more effective type-1 ryanodine receptor channel agonist under reducing conditions.
authors.affiliation: Unité Inserm 836, Grenoble Institute of Neuroscience, Site Santé, BP 170, 38042 Grenoble, France. michel.ronjat@ujf-grenoble.fr
authors.forename: Michel
authors.initials: M
authors.lastname: Ronjat
authors.forename: José Pablo
authors.initials: JP
authors.lastname: Finkelstein
authors.forename: Paola
authors.initials: P
authors.lastname: Llanos
authors.forename: Luis
authors.initials: L
authors.lastname: Montecinos
authors.forename: Hicham
authors.initials: H
authors.lastname: Bichraoui
authors.forename: Michel
authors.initials: M
authors.lastname: De Waard
authors.forename: Cecilia
authors.initials: C
authors.lastname: Hidalgo
authors.forename: Ricardo
authors.initials: R
authors.lastname: Bull
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D022162:Cytoplasmic Vesicles / Q000378:metabolism*; D004229:Dithiothreitol / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D008051:Lipid Bilayers / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000502:physiology*; D010084:Oxidation-Reduction; D011485:Protein Binding / Q000187:drug effects; D011817:Rabbits; D012433:Ryanodine / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D012604:Scorpion Venoms / Q000494:pharmacology*; D013849:Thimerosal / Q000494:pharmacology
chemical_list: D008051:Lipid Bilayers; D019837:Ryanodine Receptor Calcium Release Channel; D012604:Scorpion Venoms; C406406:maurocalcine; D012433:Ryanodine; D013849:Thimerosal; D002118:Calcium; D004229:Dithiothreitol