Background: Cardiomyocyte surface morphology and T-tubular structure are significantly disrupted in chronic heart failure, with important functional sequelae, including redistribution of sarcolemmal β(2)-adrenergic receptors (β(2)AR) and localized secondary messenger signaling. Plasticity of these changes in the reverse remodeled failing ventricle is unknown. We used AAV9.SERCA2a gene therapy to rescue failing rat hearts and measured z-groove index, T-tubule density, and compartmentalized β(2)AR-mediated cAMP signals, using a combined nanoscale scanning ion conductance microscopy-Förster resonance energy transfer technique.
Methods and results: Cardiomyocyte surface morphology, quantified by z-groove index and T-tubule density, was normalized in reverse-remodeled hearts after SERCA2a gene therapy. Recovery of sarcolemmal microstructure correlated with functional β(2)AR redistribution back into the z-groove and T-tubular network, whereas minimal cAMP responses were initiated after local β(2)AR stimulation of crest membrane, as observed in failing cardiomyocytes. Improvement of β(2)AR localization was associated with recovery of βAR-stimulated contractile responses in rescued cardiomyocytes. Retubulation was associated with reduced spatial heterogeneity of electrically stimulated calcium transients and recovery of myocardial BIN-1 and TCAP protein expression but not junctophilin-2.
Conclusions: In summary, abnormalities of sarcolemmal structure in heart failure show plasticity with reappearance of z-grooves and T-tubules in reverse-remodeled hearts. Recovery of surface topology is necessary for normalization of β(2)AR location and signaling responses.