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

Carlos A Valverde,Dmytro Kornyeyev,Alicia R Mattiazzi,Ariel L Escobar

doi:10.1016/j.bpj.2008.12.2982

Carlos A Valverde, Dmytro Kornyeyev + Show 2 more

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https://doi.org/10.1016/j.bpj.2008.12.2982

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Abstract

After a brief ischemic insult, a sustained contractile dysfunction occurs manifested as a sluggish recovery of pump function (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 fluorescent dyes (Rhod-2 or Mag-Fluo-4 to assess cytosolic or SR Ca2+, respectively). The results indicated an initial increase in diastolic Ca2+ during early R that gradually returned to pre-ischemic levels. 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, confirmed that SR Ca2+ content was greatly diminished at the onset of R and gradually recovered within 10 min of R. The present findings indicate that the increase in diastolic Ca2+ that occurs upon R is due to a SR Ca2+ release and not just because of the Ca2+ entry through the reverse NCX mode, as has been previously thought.

Highlights

2826-Plat Mutant Ryanodine Receptor-dependent Calcium Leak, RyR2 Open Probability, Calcium Sparks And Cardiac Arrhythmogenesis Stephan E
Mutations in RYR2, the gene encoding for the cardiac ryanodine receptor (RyR2), are associated with Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT), an arrhythmogenic syndrome characterized by the development of adrenergically-mediated ventricular tachycardia in individuals with an apparently normal heart
CPVT-associated mutations are proposed to result in hyperactive RyR2 channels that ‘‘leak’’ Ca2þ excessively during diastole, creating a favorable substrate for the development of tachyarrhythmias; the vast majority of RYR2 mutations (~70) fall within three domains of the RyR2 protein that control several aspects of channel function, including Ca2þ regulation, phosphorylation, e-c coupling, and FKBP12.6 interaction, among others, a single molecular mechanism of arrhythmogenesis appears unlikely

Summary

Introduction

2826-Plat Mutant Ryanodine Receptor-dependent Calcium Leak, RyR2 Open Probability, Calcium Sparks And Cardiac Arrhythmogenesis Stephan E. 2824-Plat The Origin of Antimicrobial Resistance and Fluidity Dependent Membrane Structural Transformation by Antimicrobial Peptide Protegrin-1 Matthew R. These results agree with other studies in which membrane lysis by antimicrobial peptide occurs preferentially at temperatures above the liquid crystal-gel phase transition of the lipid bilayers.

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