Reperfusion Causes Cytosolic Calcium Overload Due to Rapid Calcium Release from the Sarcoplasmic Reticulum

CARLOS VALVERDE; DMYTRO KORNYEYEV; MARTÍN VILA PETROFF; ALICIA R MATTIAZZI; ARIEL L ESCOBAR

New London, USA

Congreso; Gordon Research Conference 2008; 2008

Gordon Research Conference

Reperfusion Causes Cytosolic Calcium Overload Due to Rapid Calcium Release from the Sarcoplasmic Reticulum Carlos A. Valverde, Dmytro Kornyeyev, Mart¨ªn Vila Petroff, Alicia R Mattiazzi and Ariel L Escobar. After a brief ischemic insult, a sustained contractile dysfunction occurs manifested as a sluggish recovery of pump function after revascularization, commonly defined as myocardial stunning. Substantial evidence supports that myocardial dysfunction is triggered by Ca2+ overload during reperfusion (R). Previous results from different laboratories including our own, describe a cascade of events triggered by R that involves the activation of Na+/H+ and Na+/Ca2+ (NCX) exchangers, with enhanced Ca2+ influx. Whether this Ca2+ influx directly produces the increase in cytosolic Ca2+ or this increase occurs as a consequence of sarcoplasmic reticulum (SR) Ca2+ release triggered in turn by the Ca2+ influx, is not known. To address this issue, we performed 12 min of global no©flow ischemia followed by R in the isovolumic Langendorff perfused mouse heart, positioned on a Pulsed Local Field Fluorescence microscope and loaded with either the calcium indicator Rhod©2 or Mag©Fluo©4 to assess cytosolic Ca2+ or intraluminal SR Ca2+ respectively. The results indicated an initial increase in diastolic Ca2+ during early R that gradually returned to preischemic levels after 10 min of reperfusion. This increase was associated with a decrease in SR Ca2+ content that recovered within 10 min, as a mirror image of the diastolic Ca2+ profile. Additional experiments in which caffeine pulses (20 mM) were applied during preischemia, and 5 min and 10 min after R, confirmed that SR Ca2+ content was greatly diminished at the onset of R and gradually recovered after 5 min of R. The present findings indicate that the increase in diastolic Ca2+ that occurs upon R is due to a SR Ca2+ release ©which might be at least partially caused by Ca2+ influx through the reverse NCX mode©and not just because of the Ca2+ entry through this exchanger, as has been previously thought.