T-Tubule Proximity Modulates RyR Properties Figure 3. Effect of remodeling in the area adjacent to MI on Ca2+ sparks. A. Representative line scan image of Ca2+ spark recording in MI. The types of release areas are marked in blue and red for early and delayed release areas respectively. The artifact region (marked by –) was excluded for analysis. B. Whole-cell spark frequency and morphology in CTRL (Npigs = 12, ncells = 41) and MI (Npigs = 7, ncells = 33). C. Spark mass, calculated by amplitude*width*duration, and spark-mediated Ca2+ leak, calculated by spark frequency*spark mass, in CTRL (Npigs = 12, ncells = 41) and MI (Npigs = 7, ncells = 33). D. SR Ca2+ content as mmoles/L accessible cytosol, in CTRL (Npigs = 4, ncells = 15) and MI (Npigs = 4, ncells = 12). * denotes P,0.05. doi:10.1371/journal.pone.0025100.g003 duration tended to increase selectively in early release areas (Fig. 6C). The percentage of cells showing extremely long sparks was also significantly increased compared to CTRL (Fig. 6D). NCX current density was significantly decreased in culture, however, [Ca2+]i at that time point also tended to be lower (Fig. 6E). Taken together the data in CULT are close to what is observed in MI, but there are also differences, such as maintained SR Ca2+ content and less reduction of NCX compared to the MI group, suggesting these occur as independent events in remodeling. Discussion Heterogeneity of spark frequency in normal pig ventricular myocytes Spontaneous spark frequency was higher in early release sites implying that proximity of TTs increases RyR P0. In rat ventricular myocytes, spontaneous Ca2+ spark frequency was similar throughout intact cells, but detubulation decreased spark frequency in the central regions of the cells [11,23]. In dog ventricular myocytes with a lower TT density, spontaneous sparks PLoS ONE | www.plosone.org 5 October 2011 | Volume 6 | Issue 10 | e25100