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1992 (2)
1Author    Wilhelm Hasselbach, Andrea MigalaRequires cookie*
 Title    Modulation by Ryanodine of Active Calcium Loading and Caffeine Induced Calcium Release of Heavy Sarcoplasmic Reticulum Vesicles  
 Abstract    The effect o f ATP on the calcium release channel in heavy sarcoplasmic reticulum vesicles modulated by ryanodine has been analyzed by monitoring active calcium uptake and caffeine induced calcium release under near physiological conditions. N ative as well as ryanodine reacted vesicles display a complex time course o f calcium uptake resulting in nearly complete exhaustion o f medium calcium when ATP in combination with an ATP-regenerating system, in contrast to ATP alone, or dinitrophenyl phosphate, were used to support calcium uptake. Applying o f dinitrophenyl phosphate as energy yielding substrate, not affecting channel activi­ ty, allowed to estimate the fraction o f light vesicles devoided o f calcium channels contam inat­ ing the heavy preparation as the fraction that stores calcium after the preparation has been treated with channel opening, low concentrations o f ryanodine (1 jim). Calcium uptake by contam inant light vesicles (25%) cannot account for calcium storage, as well as, abolition o f caffeine induced calcium release o f ryanodine treated heavy vesicles. Calcium uptake o f native and ryanodine treated vesicles is accompanied by the uptake o f equivalent amounts o f inor­ ganic phosphate arising from ATP hydrolysis indicating that calcium is mainly stored as cal­ cium phosphate. The momentary capability o f the preparation to accumulate calcium was measured by activating calcium uptake during the calcium storage period with 0.2 m M 45CaCl2 and 4 m M phosphate at short time intervals. A significant increase o f the momentary uptake activity with time was observed being more pronounced for ryanodine treated than for native vesicles indicating that under regenerating conditions, A TP can induce closing o f the native and even more effectively o f the ryanodine modified calcium release channels. 
  Reference    Z. Naturforsch. 47c, 429 (1992); received December 4 1991/March 16 1992 
  Published    1992 
  Keywords    Sarcoplasmic Reticulum, Caffeine Induced Calcium Release, Ryanodine 
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 TEI-XML for    default:Reihe_C/47/ZNC-1992-47c-0429.pdf 
 Identifier    ZNC-1992-47c-0429 
 Volume    47 
2Author    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