Potentiation of Ca(2+) release by cADP-ribose in the heart is mediated by enhanced SR Ca(2+) uptake into the sarcoplasmic reticulum.
cADP-Ribose (cADPR) is a novel endogenous messenger that is believed to mobilize Ca(2+) from ryanodine-sensitive Ca(2+) stores. Despite intense research, the precise mechanism of action of cADPR remains uncertain, and experimental findings are contradictory. To elucidate the mechanism of cADPR action, we performed confocal Ca(2+) imaging in saponin-permeabilized rat ventricular myocytes. Exposure of the cells to cADPR resulted in a slow (>2 minutes) and steady increase in the frequency of Ca(2+) sparks. These effects on local release events were accompanied by a significant increase in sarcoplasmic reticulum (SR) Ca(2+) content. In comparison, sensitization of ryanodine receptors (RyRs) by caffeine, a true RyR agonist, caused a rapid (<1 second) and transient potentiation of Ca(2+) sparks followed by a decrease in SR Ca(2+) content. When the increase in the SR load was prevented by partial inhibition of the SR Ca(2+) with thapsigargin, cADPR failed to produce any increase in sparking activity. cADPR had no significant impact on activity of single cardiac RyRs incorporated into lipid bilayers. However, it caused a significant increase in the rate of Ca(2+) uptake by cardiac SR microsomes. Our results suggest that the primary target of cADPR is the SR Ca(2+) uptake mechanism. Potentiation of Ca(2+) release by cADPR is mediated by increased accumulation of Ca(2+) in the SR and subsequent luminal Ca(2+)-dependent activation of RyRs.
Lukyanenko
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V
Department of Physiology, Texas Tech University Health Sciences Center, Texas Tech University, Lubbock, Texas, USA.
Györke
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I
Wiesner
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TF
Györke
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S
D000246:Adenosine Diphosphate Ribose / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000493:pharmacokinetics; D020013:Calcium Signaling / Q000187:drug effects; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002463:Cell Membrane Permeability / Q000187:drug effects; D036563:Cyclic ADP-Ribose; D004285:Dogs; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008051:Lipid Bilayers / Q000378:metabolism; D008297:Male; D008861:Microsomes / Q000737:chemistry / Q000378:metabolism; D009206:Myocardium / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D012503:Saponins / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D019284:Thapsigargin / Q000037:antagonists & inhibitors / Q000494:pharmacology
D008051:Lipid Bilayers; D019837:Ryanodine Receptor Calcium Release Channel; D012503:Saponins; D036563:Cyclic ADP-Ribose; D000246:Adenosine Diphosphate Ribose; D019284:Thapsigargin; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D002118:Calcium