title: Luminal Ca2+ controls activation of the cardiac ryanodine receptor by ATP.
abstract: The synergic effect of luminal Ca(2+), cytosolic Ca(2+), and cytosolic adenosine triphosphate (ATP) on activation of cardiac ryanodine receptor (RYR2) channels was examined in planar lipid bilayers. The dose-response of RYR2 gating activity to ATP was characterized at a diastolic cytosolic Ca(2+) concentration of 100 nM over a range of luminal Ca(2+) concentrations and, vice versa, at a diastolic luminal Ca(2+) concentration of 1 mM over a range of cytosolic Ca(2+) concentrations. Low level of luminal Ca(2+) (1 mM) significantly increased the affinity of the RYR2 channel for ATP but without substantial activation of the channel. Higher levels of luminal Ca(2+) (8-53 mM) markedly amplified the effects of ATP on the RYR2 activity by selectively increasing the maximal RYR2 activation by ATP, without affecting the affinity of the channel to ATP. Near-diastolic cytosolic Ca(2+) levels (<500 nM) greatly amplified the effects of luminal Ca(2+). Fractional inhibition by cytosolic Mg(2+) was not affected by luminal Ca(2+). In models, the effects of luminal and cytosolic Ca(2+) could be explained by modulation of the allosteric effect of ATP on the RYR2 channel. Our results suggest that luminal Ca(2+) ions potentiate the RYR2 gating activity in the presence of ATP predominantly by binding to a luminal site with an apparent affinity in the millimolar range, over which local luminal Ca(2+) likely varies in cardiac myocytes.
authors.affiliation: Institute of Molecular Physiology and Genetics, Centre of Excellence for Cardiovascular Research, Slovak Academy of Sciences, 833 34 Bratislava, Slovak Republic.
authors.forename: Barbora
authors.initials: B
authors.lastname: Tencerová
authors.forename: Alexandra
authors.initials: A
authors.lastname: Zahradníková
authors.forename: Jana
authors.initials: J
authors.lastname: Gaburjáková
authors.forename: Marta
authors.initials: M
authors.lastname: Gaburjáková
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000494:Allosteric Regulation; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D020013:Calcium Signaling; D003600:Cytosol / Q000378:metabolism; D015640:Ion Channel Gating; D032383:Myocytes, Cardiac / Q000378:metabolism; D051381:Rats; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
chemical_list: D002120:Calcium Channel Agonists; D019837:Ryanodine Receptor Calcium Release Channel; D000255:Adenosine Triphosphate; D002118:Calcium