Salazar-Cantu A.,Monterrey Institute of Technology |
Perez-Trevino P.,Monterrey Institute of Technology |
Montalvo-Parra D.,Monterrey Institute of Technology |
Balderas-Villalobos J.,CINVESTAV |
And 5 more authors.
Archives of Biochemistry and Biophysics | Year: 2016
In Ca2+-overloaded ventricular myocytes, SERCA is crucial to steadily achieve the critical sarcoplasmic reticulum (SR) Ca2+ level to trigger and sustain Ca2+ waves, that propagate at constant rate (ʋwave). High luminal Ca2+ sensitizes RyR2, thereby increasing Ca2+ sparks frequency, and the larger RyR2-mediated SR Ca2+ flux (dF/dt) sequentially activates adjacent RyR2 clusters. Recently, it was proposed that rapid SERCA Ca2+ reuptake, ahead of the wave front, further sensitizes RyR2, increasing ʋwave. Nevertheless, this is controversial because rapid cytosolic Ca2+ removal could instead impair RyR2 activation. We assessed whether rapid SR Ca2+ uptake enhances ʋwave by changing SERCA activity (ҡDecay) over a large range (∼175%). We used normal (Ctrl) and hyperthyroid rat (HT; reduced phospholamban by ∼80%) myocytes treated with thapsigargin or isoproterenol (ISO). We found that ʋwave and dF/dt had a non-linear dependency with ҡDecay, while Ca2+ waves amplitude was largely unaffected. Furthermore, SR Ca2+ also showed a non-linear dependency with ҡDecay, however, the relationships ʋwave vs. SR Ca2+ and ʋwave vs. dF/dt were linear, suggesting that high steady state SR Ca2+ determines ʋwave, while rapid SERCA Ca2+ uptake does not. Finally, ISO did not increase ʋwave in HT cells, therefore, ISO-enhanced ʋwave in Ctrl depended on high SR Ca2+. © 2016 Elsevier Inc.
Garcia N.,Basic and Translational Research Center |
Altamirano J.,Basic and Translational Research Center
Cellular Physiology and Biochemistry | Year: 2015
Background/Aims: Pressure-overload (PO) causes cardiac hypertrophy (CH), and eventually leads to heart failure (HF). HF ventricular myocytes present transverse-tubules (TT) loss or disarrangement and decreased sarcoplasmic reticulum (SR) density, and both contribute to altered Ca2+ signaling and heart dysfunction. It has been shown that TT remodeling precedes HF, however, it is unknown whether SR structural and functional remodeling also starts early in CH. Methods: Using confocal microscopy, we assessed TT (with Di-8-ANNEPS) and SR (with SR-trapped Mag-Fluo-4) densities, as well as SR fluorophore diffusion (fluorescence recovery after photobleach; FRAP), cytosolic Ca2+ signaling and ex vivo cardiac performance in a PO rat hypertrophy model induced by abdominal aortic constriction (at 6 weeks). Results: Rats developed CH, while cardiac performance, basal and upon β-adrenergic stimulation, remained unaltered. TT density decreased by ∼14%, without spatial disarrangement, while SR density decreased by ∼7%. More important, FRAP was ∼30% slower, but with similar maximum recovery, suggesting decreased SR interconnectivity. Systolic and diastolic Ca2+ signaling and SR Ca2+ content were unaltered. Conclusion: SR remodeling is an early CH event, similar to TT remodeling, appearing during compensated hypertrophy. Nevertheless, myocytes can withstand those moderate structural changes in SR and TT, preserving normal Ca2+ signaling and contractility. © 2015 S. Karger AG, Basel.
Willis B.C.,Monterrey Institute of Technology |
Salazar-Cantu A.,Monterrey Institute of Technology |
Silva-Platas C.,Monterrey Institute of Technology |
Silva-Platas C.,Basic and Translational Research Center |
And 16 more authors.
American Journal of Physiology - Heart and Circulatory Physiology | Year: 2015
Stress-induced cardiomyopathy, triggered by acute catecholamine discharge, is a syndrome characterized by transient, apical ballooning linked to acute heart failure and ventricular arrhythmias. Rats receiving an acute isoproterenol (ISO) overdose (OV) suffer cardiac apex ischemia-reperfusion damage and arrhythmia, and then undergo cardiac remodeling and dysfunction. Nevertheless, the subcellular mechanisms underlying cardiac dysfunction after acute damage subsides are not thoroughly understood. To address this question, Wistar rats received a single ISO injection (67 mg/kg). We found in vivo moderate systolic and diastolic dysfunction at 2 wk post-ISO-OV; however, systolic dysfunction recovered after 4 wk, while diastolic dysfunction worsened. At 2 wk post-ISO-OV, cardiac function was assessed ex vivo, while mitochondrial oxidative metabolism and stress were assessed in vitro, and Ca2+ handling in ventricular myocytes. These were complemented with sarco(endo)- plasmic reticulum Ca2+-ATPase (SERCA), phospholamban (PLB), and RyR2 expression studies. Ex vivo, basal mechanical performance index (MPI) and oxygen consumption rate (MVO2) were unchanged. Nevertheless, upon increase of metabolic demand, by β-adrenergic stimulation (1–100 nM ISO), the MPI versus MVO2 relation decreased and shifted to the right, suggesting MPI and mitochondrial energy production uncoupling. Mitochondria showed decreased oxidative metabolism, membrane fragility, and enhanced oxidative stress. Myocytes presented systolic and diastolic Ca2+ mishandling, and blunted response to ISO (100 nM), and all these without apparent changes in SERCA, PLB, or RyR2 expression. We suggest that post-ISO-OV mitochondrial dysfunction may underlie decreased cardiac contractility, mainly by depletion of ATP needed for myofilaments and Ca2+ transport by SERCA, while exacerbated oxidative stress may enhance diastolic RyR2 activity. © 2015 the American Physiological Society.