Abstract 14993: Alteration in b2-ARs Dependent cAMP Signalling Linked to Post Infarction Remodelling of T-tubules in Rat Cardiomyocytes
The T-tubule (TT) network of cardiomyocytes (CMs) compartmentalizes beta-2 adrenergic receptor (β2AR) signalling allowing stringent control of spread of cAMP. In heart failure these structures are disrupted, disturbing cAMP compartmentalization, with TT loss and associated changes in cAMP signalling occurring in a stepwise manner. We studied these changes at different stages of disease progression.
Ventricular CMs were isolated from post-myocardial infarction (MI) failing rats at 4 weeks (compensated), 8 and 16 weeks (decompensated). TT density, regularity, and axial junctions were determined by confocal imaging of di-8-ANNEPS stained CMs. Scanning Ion Conductance Microscopy (SICM) generated CM scans allowed assessment of topographical features. cAMP levels were determined using a FRET sensor combined with SICM. β2AR were stimulated with isoproterenol with a β1-specific antagonist CGP20712A, by whole cell perfusion, or locally via SICM nanopipette. NKH477 an adenylate cyclase (AC) activator was applied subsequently.
At 4 weeks post-MI, pronounced internal changes occurred (the TT density decreased by 14.7±.4.9%, p<0.005 and regularity decreased by 49.9±8.3%, p<0.001), while the Z-groove index was not changed. Interestingly, the amount of axial junctions increased by 41.1±12%, p<0.005. Localized cAMP response to β2AR stimulation decreased by 72.6±8.4%, p<0.001 (n≥10), while global β2AR stimulation remained unchanged. β2AR-cAMP remained confined when stimulating at TT whereas in crests of the sarcolemma it increased by 106±22.2%, p<0.001 (n≥10).
At 8 weeks structural changes progressed. TT stimulated β2AR-cAMP, formerly localized, diffused throughout the CMs.
At 16 weeks post-MI the overall structure of CMs changed, Z-groove index had diminished gradually by 29.8±4.1%, p<0.001 (n≥40). TT regularity and density were further decreased. Junctions decreased by 27.5±9.9%, p<0.01 (n=20). Global cAMP amplitude was reduced for both β2AR 48.5±9.9%, p<0.0001 (n≥24) and AC 62.6±8.4%, p<0.0001 (n≥14),as was the local β2AR-cAMP response in TT.
In conclusion, TT changes begin early after MI, whilst the functional β2AR-cAMP delocalisation develops later at a phase associated with the transition to decompensated heart failure.
- © 2013 by American Heart Association, Inc.