title: Ca2+ Sparks and Ca2+ waves are the subcellular events underlying Ca2+ overload during ischemia and reperfusion in perfused intact hearts.
abstract: Abnormal intracellular Ca(2+) cycling plays a key role in cardiac dysfunction, particularly during the setting of ischemia/reperfusion (I/R). During ischemia, there is an increase in cytosolic and sarcoplasmic reticulum (SR) Ca(2+). At the onset of reperfusion, there is a transient and abrupt increase in cytosolic Ca(2++), which occurs timely associated with reperfusion arrhythmias. However, little is known about the subcellular dynamics of Ca(2+) increase during I/R, and a possible role of the SR as a mechanism underlying this increase has been previously overlooked. The aim of the present work is to test two main hypotheses: (1) An increase diastolic Ca(2+) sparks frequency (cspf) constitutes a mayor substrate for the ischemia-induced diastolic Ca(2+) increase; (2) an increase in cytosolic Ca(2+) pro-arrhythmogenic events (Ca(2+) waves), mediates the abrupt diastolic Ca(2+) rise at the onset of reperfusion. We used confocal microscopy on mouse intact hearts loaded with Fluo-4. Hearts were submitted to global I/R (12/30 min) to assess epicardial Ca(2+) sparks in the whole heart. Intact heart sparks were faster than in isolated myocytes whereas cspf was not different. During ischemia, cspf significantly increased relative to preischemia (2.07±0.33 vs. 1.13±0.20 sp/s/100 μm, n=29/34, 7 hearts). Reperfusion significantly changed Ca(2+) sparks kinetics, by prolonging Ca(2+) sparks rise time and decreased cspf. However, it significantly increased Ca(2+) wave frequency relative to ischemia (0.71±0.14 vs. 0.38±0.06 w/s/100 μm, n=32/33, 7 hearts). The results show for the first time the assessment of intact perfused heart Ca(2+) sparks and provides direct evidence of increased Ca(2+) sparks in ischemia that transform into Ca(2+) waves during reperfusion. These waves may constitute a main trigger for reperfusion arrhythmias.
authors.affiliation: Centro de Investigaciones Cardiovasculares, CONICET-La Plata, Facultad de Medicina, UNLP, Argentina.
authors.forename: Alicia
authors.initials: A
authors.lastname: Mattiazzi
authors.affiliation: Universidad Nacional de San Martin, San Martin, Argentina; Biological Engineering and Small Scale Technologies, School of Engineering, University of California, Merced, CA, USA.
authors.forename: Mariana
authors.initials: M
authors.lastname: Argenziano
authors.affiliation: Biological Engineering and Small Scale Technologies, School of Engineering, University of California, Merced, CA, USA.
authors.forename: Yuriana
authors.initials: Y
authors.lastname: Aguilar-Sanchez
authors.affiliation: Centro de Investigaciones Cardiovasculares, CONICET-La Plata, Facultad de Medicina, UNLP, Argentina.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Mazzocchi
authors.affiliation: Biological Engineering and Small Scale Technologies, School of Engineering, University of California, Merced, CA, USA. Electronic address: aescobar4@ucmerced.edu.
authors.forename: Ariel L
authors.initials: AL
authors.lastname: Escobar
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002469:Cell Separation; D006321:Heart / Q000503:physiopathology*; D006352:Heart Ventricles / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008810:Mice, Inbred C57BL; D015428:Myocardial Reperfusion Injury / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D032383:Myocytes, Cardiac / Q000378:metabolism; D010477:Perfusion; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D012333:RNA, Messenger; D002118:Calcium
keywords: Ca(2+) sparks; Intact heart; Ischemia/reperfusion