Sarcoplasmic reticulum function abnormalities in rabbit failing hearts

In a model of heart failure induced in rabbits by a double volume plus pressure overload, sarcoplasmic reticulum (SR) function was measured by Ca uptake and ryanodine receptor analysis. When expressed per mg of proteins, Ca uptake was decreased by 20% in failing hearts (FH) and ryanodine receptor density was similar in control hearts (CH) and in FH. However Ca uptake and ryanodine receptor density were significantly increased when expressed per total left ventricle suggesting SR hypertrophy. On electron microscopic examination, SR morphology not directly examined but large hypertrophied T tubules were observed suggesting a change in the relationship between membranes and contractile apparatus which may lead to alterations in excitation-contraction-relaxation coupling in spite of minimal biochemical alterations of SR.