Reperfusion Ca2+ Waves in the Intact Heart: A Possible Trigger for the Generation of Reperfusion Arrhythmias

Abstract

Abnormal intracellular Ca2+ cycling plays a key role in cardiac dysfunction, particularly during the setting of cardiac ischaemia/reperfusion (I/R). At the onset of reperfusion there is an increase in cytosolic Ca2+, which has been usually associated with an uncontrolled influx from the extracellular space. Ca2+ mishandling has been in turn related to reperfusion arrhythmias. However, the basic mechanism for these arrhythmias is still unresolved. We performed experiments to test the hypothesis that the increase in cytosolic Ca2+ at the onset of reperfusion originates in Ca2+ efflux from the sarcoplasmic reticulum (SR) and propagates through the cell as cytosolic Ca2+ waves serving as a trigger for the initiation of reperfusion arrhythmias. By using a combination of pulsed local-field fluorescence (PLFF) and laser scanning confocal microscopy in mouse intact hearts loaded with Rhod-2 and/or Mag-Fluo-4 (cytosolic and/or SR Ca2+ measurements) or Fluo-4 (Ca2+ sparks and waves) and submitted to global I/R (12/30 min), it was found that ischemia evoked an increase in cytosolic and SR Ca2+. This increase was associated with a significant rise in Ca2+ sparks relative to preischemia: 2.07 ± 0.33 vs. 1.13 ± 0.20 sp/sec/100μm (P<0.05, ANOVA). Reperfusion evoked an increment in cytosolic Ca2+ (Ca2+ bump) that was associated with a significant decrease in SR Ca2+ and in Ca2+ sparks with respect to ischemia and a significant increase in Ca2+ waves relative to ischemia and preischemia: 0.71± 0.14 vs. 0.38± 0.06 and 0.25 ± 0.04 w/sec/100μm. The results show the first direct evidence of an increase in Ca2+ sparks in ischemia that transform in Ca2+ waves during reperfusion. These waves may constitute a main trigger of reperfusion arrhythmias. Supported by NIH R01-HL-084487 and PICT/1903 (FONCYT).