Abstract 16819: Intracellular Dyssynchrony in Ca Removal from the Cytosol In Ventricular Cardiac Myocytes
In cardiomyocytes, cytosolic Ca removal is mediated by the sarcoplasmic reticulum Ca ATPase (SERCA), sarcolemmal Na/Ca exchanger (NCX), plasmalemmal Ca ATPase and mitochondrial Ca uniporter (MCU). We report, for the first time, spatiotemporal inhomogeneities in cytosolic Ca removal in normal and diseased heart and explore underlying mechanisms. Spatially resolved Ca transients (1 Hz, Fluo-4 AM) were recorded at steady state using confocal microscopy in ventricular cardiomyocytes. The time constant of cytosolic [Ca] decay (tau_loc) of local Ca transients was quantified at 1 µm intervals across the cell. In murine cardiomyocytes tau_loc distribution was inhomogeneous, with a maximal difference between cell regions of 237±9 ms and a variation coefficient (CV_tau) of 14±2% (mean±S.E.M., n=10 cells). tau_loc was not releated to the local amplitude or release kinetics of Ca. Coherent regions of fast (fastCaR, tau_loc < mean tau of whole cell) and slow (slowCaR) Ca removal had similar widths (4.6±0.2 vs. 5.1±0.5 µm). Forskolin accelerated, and SERCA inhibitor cyclopiazonic acid (CPA) inhibited Ca removal significantly more in slowCaR than in fastCaR. In contrast, NCX-inhibitor SEA0400 slowed cytosolic Ca removal similarly in slowCaR and fastCaR. Also, CV_tau was similar in NCX+/- knock-out vs. wild-type mice, suggesting no contribution of NCX to the dyssynchrony of cytosolic Ca removal. tau_loc distribution was also inhomogenous in pig ventricular myocytes. Ca removal from the cytosol was more dyssynchronous in cardiomyocytes from chronic (4 weeks) ischemic pig myocardium (peri-infarct zone) vs. sham-operated pigs (CV_tau 24±1% vs. 20±1%, n=57 cells/group, p<0.05). Simultaneous recording of Ca transients and mitochondrial signal (mitotracker) unveiled a significant correlation between FastCaR regions and mitochondria (n=9 cells, p<0.05). Ru360 (MCU-inhibitor) slowed tau_loc more in FastCaR (to 126±12% vs. 112±10% of baseline in SlowCaR; p<0.05, n=5).
Conclusion: Cytosolic Ca removal is dyssynchronous in mouse and pig cardiomyocytes. Ca removal in chronically ischemic cardiomyocytes is more dyssynchronous, suggesting a potential new mechanism of cardiomyocyte dysfunction. Mitochondria influence the differences in local Ca reuptake.
- © 2011 by American Heart Association, Inc.