Abstract 10542: Telethonin Regulates Transverse Tubule Structure and Ca2+ Induced Ca2+ Release in Mouse Ventricular Myocytes
T tubule disruption is implicated in the pathogenesis of heart failure. The molecular regulation of t tubule structure is poorly understood. T Cap, a sarcomeric Z disc protein, has been suggested to be necessary for normal t tubule structure in skeletal muscle and can promote t tubule formation in response to increases in load. We hypothesised that T Cap is important for normal t tubule structure and Ca2+ handling in ventricular cardiomyocytes. We studied Ca2+ handling and t tubule structure in ventricular cardiomyocytes from hearts lacking T Cap (KO) at a young (<3 months) and advanced (>8 months) age compared to age matched wild type mice (WT). Using confocal microscopy in cardiomyocytes stained with Fluo 4, we observed an increase in the variance of the time to peak of the Ca2+ transient in young ((ms2) WT 297 ± 131 (n=40) vs KO 393 ± 156 (n=48) p<0.05) and old KO mice (WT 308 ± 156 (n=48) vs. KO 430 ± 165 (n=43) p<0.05) suggesting a deterioration in the regulation of the Ca2+ transient. In old animals, Ca2+ transient time to peak ((ms) WT 35 ± 20 (n=48) vs KO 95 ± 18 (n=43) p<0.01) and time to 90% decline were delayed (WT 375 ± 73 (n=43) vs. KO 460 ± 55 (n=20) p<0.05). Ca2+ spark frequency increased in young ((sp/s) WT 0.346 ± 0.35 (n=32) vs KO 0.867 ± 0.5 (n=29) p<0.05) and old KO mice (WT 0.370 ±0.3 (n=15) vs. KO 0.843 ±0.8 (n=23) p<0.01). Ca2+ spark peak was reduced in old KOs ( (F/F0) WT 1.90 ± 0.3 (n=45) vs KO 1.4 ± 0.8 (n=43) p<0.05). L type Ca2+ current density was reduced in old KOs ((pA/pF) WT 4.75 ± 0.38 (n=16) vs KO 3.37 ± 0.30 (n=20) p<0.01). The action potential morphology was unchanged. Using di 8 ANEPPS and confocal microscopy, we observed a reduced t tubule density in old KOs (36.8 ± 5 % (n=45) vs. 30.2 ± 4 % (n=44) p<0.05). We assessed t tubule regularity using a Fourier analysis and found a less regular t tubule structure in both young ((power of dominant peak) WT 2.350 ± 1.09 (n=30) vs KO 1.570 ± 1.06 (n=32) and old (WT 2.10 ± 1.10 (n=39) vs KO 1.30 ± 1.0 (n=20) p<0.05) KO animals. Scanning ion conductance microscopy showed a loss of cell surface structure in old KO animals ((z groove index) WT: 0.8 ± 0.03 vs KO: 0.6 ± 0.05, p<0.01). T tubule disarray may explain the changes to Ca2+ homeostasis observed. T Cap is essential for normal t tubule structure and CICR in ventricular cardiomyocytes.
- © 2011 by American Heart Association, Inc.