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Keywords:

  • inline image handling;
  • echocardiography;
  • isolated hearts;
  • metabolic syndrome;
  • SERCA2a

Abstract

Aim

Various components of metabolic syndrome associate with cardiac intracellular calcium (inline image) mishandling, a precipitating factor in the development of heart failure. We aimed to provide a thorough description of early stage inline image-cycling alterations in the fructose-fed rat, an experimental model of the disorder, where insulin resistance, hypertension and dyslipidaemia act cooperatively on the heart.

Method

Rats were fed with fructose-rich chow. After 6 weeks, echocardiography was performed, which was followed by measurements of myocardial inline image transients recorded by Indo-1 surface fluorometry in isolated perfused hearts. Sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA2a) activity was assessed by administration of its inhibitor cyclopiazonic acid (CPA). Mathematical model analysis of inline image transients was used to estimate kinetic properties of SR Ca2+ transporters. Protein levels of key Ca2+ handling proteins were also measured.

Results

Echocardiography showed signs of cardiac hypertrophy, but in vivo and ex vivo haemodynamic performance of fructose-fed rat hearts were unaltered. However, a decline in Ca2+ sequestration capacity (inline image and decay time of inline image transients) was observed. Model estimation showed decreased affinity for Ca2+ (higher Km) and elevated Vmax for SERCA2a. Diseased hearts were more vulnerable to CPA application. Fructose feeding caused elevation in SERCA2a and phosphorylated phospholamban (PLB) expression, while total PLB level remained unchanged.

Conclusion

In early stage, metabolic syndrome primarily disturbs SERCA2a function in the heart, but consequential haemodynamic dysfunction is prevented by upregulation of SERCA2a protein level and phosphorylation pathways regulating PLB. However, this compensated state is very vulnerable to a further decline in SERCA2a function.