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Regulation of the calcium release channel from rabbit skeletal muscle by the nucleotides ATP, AMP, IMP and adenosine

Laver, Derek Rowland; Lenz, Gerlende; Lamb, Graham

Description

1. Nucleotide activation of skeletal muscle ryanodine receptors (RyRs) was studied in planar lipid bilayers in order to understand RyR regulation in vivo under normal and fatigued conditions. With 'resting' calcium (100 nM cytoplasmic and 1 mM luminal), RyRs had an open probability (Po) of ∼0.01 in the absence of nucleotides and magnesium. ATP reversibly activated RyRs with Po at saturation (Pmax) ∼0.33 and Ka (concentration for half-maximal activation) ∼0.36 mM and with a Hill coefficient (nH)...[Show more]

dc.contributor.authorLaver, Derek Rowland
dc.contributor.authorLenz, Gerlende
dc.contributor.authorLamb, Graham
dc.date.accessioned2015-12-13T22:15:44Z
dc.date.available2015-12-13T22:15:44Z
dc.identifier.issn0022-3751
dc.identifier.urihttp://hdl.handle.net/1885/70536
dc.description.abstract1. Nucleotide activation of skeletal muscle ryanodine receptors (RyRs) was studied in planar lipid bilayers in order to understand RyR regulation in vivo under normal and fatigued conditions. With 'resting' calcium (100 nM cytoplasmic and 1 mM luminal), RyRs had an open probability (Po) of ∼0.01 in the absence of nucleotides and magnesium. ATP reversibly activated RyRs with Po at saturation (Pmax) ∼0.33 and Ka (concentration for half-maximal activation) ∼0.36 mM and with a Hill coefficient (nH) of ∼1.8 in RyRs when Pmax < 0.5 and ∼4 when Pmax > 0.5. 2. AMP was a much weaker agonist (Pmax ∼0.09) and adenosine was weaker still (Pmax ∼0.01-0.02), whereas inosine monophosphate (IMP), the normal metabolic end product of ATP hydrolysis, produced no activation at all. 3. Adenosine acted as a competitive antagonist that reversibly inhibited ATP- and AMP-activated RyRs with nH ∼ and Ki ∼0.06 mM at [ATP] < 0.5 mM, increasing 4-fold for each 2-fold increase in [ATP] above 0.5 mM. This is explained by the binding of a single adenosine preventing the cooperative binding of two ATP or AMP molecules, with dissociation constants of 0.4, 0.45 and 0.06 mM for ATP, AMP and adenosine, respectively. Importantly, IMP (≤ 8 mM) had no inhibitory effect whatsoever on ATP-activated RyRs. 4. Mean open (τo) and closed (τc) dwell-times were more closely related to Po than to the nucleotide species or individual RyRs. At Po < 0.2, RyR regulation occurred via changes in τc, whereas at higher Po this also occurred via changes in τo. The detailed properties of activation and competitive inhibition indicated complex channel behaviour that could be explained in terms of a model involving interactions between different subunits of the RyR homotetramer. 5. The results also show how deleterious adenosine accumulation is to the function of RyRs in skeletal muscle and, by comparison with voltage sensor-controlled Ca2+ release, indicate that voltage sensor activation requires ATP binding to the RyR to be effective.
dc.publisherCambridge University Press
dc.sourceJournal of Physiology
dc.subjectKeywords: adenosine; adenosine phosphate; adenosine triphosphate; calcium channel; inosine phosphate; magnesium; nucleotide; protein subunit; ryanodine receptor; tetramer; animal cell; animal tissue; article; binding competition; calcium transport; cell membrane st
dc.titleRegulation of the calcium release channel from rabbit skeletal muscle by the nucleotides ATP, AMP, IMP and adenosine
dc.typeJournal article
local.description.notesImported from ARIES
local.description.refereedYes
local.identifier.citationvolume537
dc.date.issued2001
local.identifier.absfor060104 - Cell Metabolism
local.identifier.ariespublicationMigratedxPub2340
local.type.statusPublished Version
local.contributor.affiliationLaver, Derek Rowland, College of Medicine, Biology and Environment, ANU
local.contributor.affiliationLenz, Gerlende, College of Medicine, Biology and Environment, ANU
local.contributor.affiliationLamb, Graham, La Trobe University
local.bibliographicCitation.issue3
local.bibliographicCitation.startpage763
local.bibliographicCitation.lastpage778
local.identifier.doi10.1113/jphysiol.2001.012775
dc.date.updated2015-12-11T07:19:48Z
local.identifier.scopusID2-s2.0-0035893823
CollectionsANU Research Publications

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