Changes in T-tubules and sarcoplasmic reticulum in ventricular myocytes in early cardiac hypertrophy in a pressure overload rat model
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© 2015 S. Karger AG, Basel. 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 Ca 2+ 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 Ca 2+ 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 ß-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 Ca 2+ signaling and SR Ca 2+ 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 Ca 2+ signaling and contractility.