Simulated ischemia does not mimic stop flow ischemia in perfused mouse hearts

SALAS NEHUEN; ALICIA MATTIAZZI; GABRIELA MAZZOCCHI; CARLOS VALVERDE

Buenos Aires

Congreso; XXII World Congress of the ISHR; 2016

INTERNATIONAL SOCIETY FOR HEART RESEARCH

Introduction: Cardiac ischemia is a pathological condition in which the blood supply to the myocardium is interrupted. This loss of circulation leads to the impairment of cardiac mechanical and electrical function. Still, the role of Ca2+ underlying these dysfunctions is not fully understood. To identify the ionic alterations that occurred during ischemia, several laboratories appealed to the use of ischemia-like conditions (hypoxia-metabolic inhibition-acidification), in isolated myocytes. However, whether simulated ischemia (SI) actually mimics stop-flow ischemia (SFI) at the cellular level, has not been previously explored and is the aim of the present work. Methods: Hearts from Balb/c mice were perfused (Langendorff technique), at constant flow/temperature. Left-ventricle developed pressure, LVDP, and LV-end-diastolic pressure, LVEDP, were assessed with a latex balloon connected to a pressure transducer. Cytosolic Ca2+ was assessed in Rhod-2-loaded hearts in a pulsed-local-field fluorescence microscope. Action potentials (AP) were registered with microelectrodes. Phosphorylation of phospholamban (PLN), known to occur at the onset of reperfusion, was assessed by western blot. Hearts were submitted to 15min of either SFI or SI (pH 6.2, absence of glucose, N2 instead of O2). Results: SI produced a milder mechanical dysfunction than SFI. Similarly, Ca2+ transient and AP amplitude were lower during ischemia in SFI than in SI. Upon reperfusion, the mechanical recovery of LVDP was significantly more pronounced in SI than in FR-hearts (LVDP: 48.5±6.2 vs. 11.9±6.6% of preischemic value; LVEDP: 29.0±5.5 vs. 56.6±3.1mmHg, respectively), whereas PLN phosphorylation by CaMKII at early reperfusion was higher in SFI than in SI hearts (812±46 vs. 155±26%). No changes were observed in PLN-Ser16-phosphorylation in any of these conditions. Conclusion: SI generates a milder alteration of mechanical and Ca2+ handling when compared to SFI. The findings indicate that SI results have to be interpreted with caution and underscore the use of SFI to assess intracellular Ca2+ during ischemia/reperfusion.