Cardiac remodeling and end-stage heart failure were associated with increased variation in local cytosolic Ca2+ decay time constants in murine, porcine, and human ventricular cardiomyocytes.
Dyssynchronous intracellular [Ca2+] decay is increased in cardiac remodeling and heart failure, suggesting a novel mechanism for cellular contractile dysfunction.
RATIONALE: Synchronized release of Ca²⁺ into the cytosol during each cardiac cycle determines cardiomyocyte contraction. OBJECTIVE: We investigated synchrony of cytosolic Ca²⁺ decay during diastole and the impact of cardiac remodeling. METHODS AND RESULTS: Local cytosolic Ca²⁺ transients (1-µm intervals) were recorded in murine, porcine, and human ventricular single cardiomyocytes. We identified intracellular regions of slow (slowCaR) and fast (fastCaR) Ca²⁺ decay based on the local time constants of decay (TAUlocal). The SD of TAUlocal as a measure of dyssynchrony was not related to the amplitude or the timing of local Ca²⁺ release. Stimulation of sarcoplasmic reticulum Ca²⁺ ATPase with forskolin or istaroxime accelerated and its inhibition with cyclopiazonic acid slowed TAUlocal significantly more in slowCaR, thus altering the relationship between SD of TAUlocal and global Ca²⁺ decay (TAUglobal). Na⁺/Ca²⁺ exchanger inhibitor SEA0400 prolonged TAUlocal similarly in slowCaR and fastCaR. FastCaR were associated with increased mitochondrial density and were more sensitive to the mitochondrial Ca²⁺ uniporter blocker Ru360. Variation in TAUlocal was higher in pig and human cardiomyocytes and higher with increased stimulation frequency (2 Hz). TAUlocal correlated with local sarcomere relengthening. In mice with myocardial hypertrophy after transverse aortic constriction, in pigs with chronic myocardial ischemia, and in end-stage human heart failure, variation in TAUlocal was increased and related to cardiomyocyte hypertrophy and increased mitochondrial density. CONCLUSIONS: In cardiomyocytes, cytosolic Ca²⁺ decay is regulated locally and related to local sarcomere relengthening. Dyssynchronous intracellular Ca²⁺ decay in cardiac remodeling and end-stage heart failure suggests a novel mechanism of cellular contractile dysfunction.
Hohendanner et al. (Thu,) conducted a other in Cardiac remodeling and human heart failure. Cardiac remodeling and heart failure vs. Normal cardiomyocytes was evaluated on Variation in local time constants of cytosolic [Ca2+] decay (TAUlocal). Cardiac remodeling and end-stage heart failure were associated with increased variation in local cytosolic Ca2+ decay time constants in murine, porcine, and human ventricular cardiomyocytes.