Abstract 13130: Age-associated Reductions in Junctophilin-2 and Amphiphysin-2 Associate With Disruption of T-tubules and Intracellular Calcium Regulation in Myocytes From the Mouse Left Ventricle
With progressive aging cardiac contractile performance declines. Our hypothesis was that this dysfunction is contributed to by aging-related ultra structural changes in cardiac myocytes. Single myocytes were obtained from the left ventricle of male C57Bl6 mice at the ages of 6, 12, 18 and 24 months, covering the majority of the lifespan. Di-8-Anepps labelling was used to visualize membrane structures, and whole-cell patch clamp to assess membrane capacitance. An age-correlated hypertrophy was evident. Cell width increased by a total of 41.4±0.3% (mean±SD) and cell length by 20.3±0.2% across the age range studied (n=82 cells from 7 hearts at each age, p<0.01 by ANOVA) indicating progressive concentric and eccentric hypertrophy. Accompanying this an 18.4±2.5% reduction in T-tubule density was identified between the ages of 6 and 24 months (p<0.01), despite a 36±18% rise in cell capacitance. At the microstructure level T-tubule arrangement also changed with transverse-orientated T-tubules falling 39±11%, whilst longitudinal T-tubules increased 9±4% (6 vs. 24 months, p<0.01 in each case). Accompanying this remodeling western blot analysis found amphiphysin-2, involved in T-tubule formation, and, junctophilin-2, key for associating sarcoendoplasmic reticulum with T-tubules, were both significantly reduced in left ventricular tissue at 24 months of age by 63±17% and 57±18% respectively compared with tissue from animals at 6 months (both p<0.01, n=7). Functionally time to peak of the calcium transient in field-stimulated myocytes, was prolonged by 36±12% in myocytes from animals at 24 months compared with that observed in cells from 6 month old animals (n=7 cells from 6 animals at each age p=0.01, by ANOVA). In localized regions of individual myocytes from aged animals reduced T-tubule density associated with even greater localized delays in the rise of the transient. Overall there was greater heterogeneity in the calcium rise across myocytes from aged animals compared with the essentially synchronous rise seen in those from young (6 month) animals. In conclusion aging associates with myocyte hypertrophy and T-tubule disruption, in turn associating with disruption of cellular calcium control.
Author Disclosures: L. Cheah: None. M.K. Lancaster: None.
- © 2015 by American Heart Association, Inc.