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1992 (2)
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1Author    M. Artina, U. Ngeheuer, A.Ndrea Migala, Wilhelm HasselbachRequires cookie*
 Title    Is the Calcium Pump Involved in Calcium Release?  
 Abstract    The blockage of all thiol residues accessible to the mercurial mersalyl in the sarcoplasmic reticulum m em branes resulting in complete inactivation of the m em branes' calcium transport system does interfere neither with caffeine-nor calcium-induced calcium release from actively loaded mem brane vesicles. In troduction 
  Reference    Z. Naturforsch. 41c, 647—651 (1986); received March 18 1986 
  Published    1986 
  Keywords    Sarcoplasmic Reticulum, Calcium Release, Caffeine, Thiol Blockage 
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 TEI-XML for    default:Reihe_C/41/ZNC-1986-41c-0647.pdf 
 Identifier    ZNC-1986-41c-0647 
 Volume    41 
2Author    Wilhelm Hasselbach, Andrea MigalaRequires cookie*
 Title    Interaction of Ryanodine with the Calcium Releasing System of Sarcoplasmic Reticulum Vesicles  
 Abstract    Heavy sarcoplasmic reticulum vesicles were reacted with ryanodine in 0.6 M KCl 0.3 M sucrose at pH 6.3 and pH 7.0 at 20 °C. The inhibition of caffeine induced calcium release from actively loaded vesicles by ryanodine was applied to monitor time course and attainment of equilibrium of the interaction of ryanodine with its receptors in the vesicular membranes. At ryanodine concentrations rising from 0.1-100 | XM, the logarithms of the release amplitudes linearly decline with time. The dependence of the inactivation reaction on the concentration of ryanodine did not saturate in the applicable concentration range. The reaction halflife times are concentration dependent. At pH 7.0, the half times decline from 100 to 10 s when the ryanodine concentration is raised from 0.1 to 1 [J, M. At pH 6.3 a corresponding decline occurs between 3 (XM and 100 | AM. The marked dependence of the inactivation reaction on medium pH requires reaction times of one and five hours at pH 7.0 and 6.3, respectively for the attainment of reaction equilib-rium at low ryanodine concentrations. The dependence of the amplitude of calcium release on the concentration of added ryanodine has been evaluated as proposed by Gutfreund (Enzymes: Physical Principles, p. 71, Wiley-Interscience, London 1972) for the preparation's affinity for ryanodine and its number of binding sites. At pH 7.0, preparations appear to contain only 0.7 pmol sites per mg protein having an affinity for ryanodine of 0.33 nM"'. The titration curves for caffeine induced calcium release, initial calcium uptake and final calcium level are identical, indicating that the three functions are controlled by the same receptor. Calcium induced calcium release, however, is only partially and differently affected by the occupancy of the high affinity ryanodine binding sites. The kinetic and equilibrium data for the effects of ryanodine were combined and analyzed on account of a two step reaction sequence. The corresponding dissociation and rate constants were evaluated and combined with reported data of [ 3 H]ryanodine binding (Pessah et al., J. Biol. Chem. 261, 8643-8648 (1986)). 
  Reference    Z. Naturforsch. 43c, 140—148 (1988); received November 4 1987 
  Published    1988 
  Keywords    Sarcoplasmic Reticulum Ryanodine, Caffeine, Calcium Release 
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 TEI-XML for    default:Reihe_C/43/ZNC-1988-43c-0140.pdf 
 Identifier    ZNC-1988-43c-0140 
 Volume    43 
3Author    Wilhelm Hasselbach, Andrea MigalaRequires cookie*
 Title    How Many Ryanodine Binding Sites Are Involved in Caffeine Induced Calcium Release from Sarcoplasmic Reticulum Terminal Cysternae Vesicles?  
 Abstract    The inhibition by ryanodine of caffeine induced calcium release from actively loaded heavy sarcoplasmic vesicles has been studied in order to analyse the relation between the occupancy of the vesicular calcium release channels by ryanodine and channel function. Ryanodine bind­ ing was monitored with [3H]ryanodine under ionic conditions favouring the establishment of binding equilibrium. Binding follows 1 : 1 stoichiometry yielding dissociations constants be­ tween 7 — 12 nM and 12-15 pmol ryanodine/mg vesicular protein as maximum number of ryanodine binding sites. When ryanodine labeling was monitored by measuring the decline of the amplitude of caffeine induced calcium release 50% inhibition occurred at a free ryanodine concentration of 1 nM. At this concentration less than 10% of the available ryanodine binding sites are occupied. Caffeine induced calcium release is completely abolished when 3 pmol ryanodine/mg have reacted. A corresponding divergence between ryanodine binding and its effect on caffeine induced calcium release was observed when the initial rate of ryanodine binding was measured either by labeling the vesicles with [3H]ryanodine or by following the decline with time of caffeine induced calcium release. Caffein induced calcium release declines four times faster than the fraction of unoccupied ryanodine binding sites, k = 4.3 x 104 m -1 s_1 versus 1.2 x 104 M" 1 s-1. The observed interrelation between the occupation of ryanodine bind­ ing sites and its effect on caffeine induced calcium release indicates that the caffeine sensitive calcium channel functions as an assembly of at least 4 ryanodine binding sites whereby the occupation of one site suffices to abolish calcium release. The stoichiometric composition ap­ pears to be not fixed but might change according to the size of the fraction of ryanodine recep­ tors exhibiting caffeine sensitivity. The reported data were evaluated according to the algo­ rithm derived by H. Asai and M. F. Morales, J. Biol. Chem. 4, 830-838 (1965) for the activity of a macromolecule and the extent of an inhibiting reaction. 
  Reference    Z. Naturforsch. 47c, 136—147 (1992); received August 7 1991 
  Published    1992 
  Keywords    Sarcoplasmic Reticulum, Caffeine, Calcium Release, Ryanodine Binding 
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 TEI-XML for    default:Reihe_C/47/ZNC-1992-47c-0136.pdf 
 Identifier    ZNC-1992-47c-0136 
 Volume    47 
4Author    Wilhelm Hasselbach, Andrea MigalaRequires cookie*
 Title    Modulation by Monovalent Anions of Calcium and Caffeine Induced Calcium Release from Heavy Sarcoplasmic Reticulum Vesicles  
 Abstract    Both calcium and caffeine induced calcium release from actively loaded heavy sarcoplasmic reticulum vesicles were studied to analyze the dependence o f both activities on the com position o f the release medium with respect to monovalent anions. Calcium is unable to induce net cal­ cium release while caffeine remains effective as releasing agent when the experimental media contain neither chloride nor nitrate ions. Caffeine induced calcium release is not suppressed by chelating residual medium calcium (approximately 0 .5 -1 (j m) with 2 m M EGTA added 15 s prior to 10 m M caffeine. Calcium release from vesicles loaded in media containing 0.2 m glu­ conate as monovalent anion is induced when the medium is supplemented with chloride or nitrate. The release amplitude increases linearly when K-gluconate is replaced by KC1. At con­ stant ionic strength the release amplitude becomes maximal at a chloride concentration o f 0.2 m . The chloride effect com pletely disappears when 2 m M EGTA are added simultaneously. When chloride is replaced by nitrate, as releasing agent, maximal release is achieved already by addition o f 0.1 m K-nitrate. The releasing effect o f nitrate can only partially be suppressed by EGTA. The different effectiveness o f gluconate, chloride and nitrate as calcium release sup­ porting ions corresponds to their activating effect on the binding o f ryanodine to the calcium release channel in the vesicular membranes. 
  Reference    Z. Naturforsch. 47c, 440 (1992); received December 4 1991/March 16 1992 
  Published    1992 
  Keywords    Sarcoplasmic Reticulum, Calcium Release, Chloride, Nitrate, Ryanodine 
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 TEI-XML for    default:Reihe_C/47/ZNC-1992-47c-0440.pdf 
 Identifier    ZNC-1992-47c-0440 
 Volume    47