Figure 3: (A) Top, Epi-illumination image of an intact cardiomyocyte treated with anti-α 1B-adrenergic receptor antibody (sc-27136, Santa Cruz, CA; see [38]) QDs at 3 nM in oxygenated Ca2+-free-HEPES-Tyrode’s solution containing 20 mM 2,3-butane-dione monoxime at 25°C (see [25]). Note the periodic fluorescent profiles of QDs along the myocyte. Bottom, enlarged view of the area shown in the rectangular outline in the top of this figure. (a), (b), and (c) indicate the regions within the myocyte used for the length analyses in (B). (B) Analysis of the distance (indicated by the number below each graph) between the QD fluorescence signals in (a), (b), and (c) in (a). Analysis was conducted based on [25]. We found that the values differed for two sequential distances, that is, 1.73 and 1.51 μm, respectively, in (a) and (b). The inhomogeneity of the length of the sarcomere in series may induce nonlinear phenomena such as SPOC upon activation (see [30]), because the ~0.2 μm difference in SL can affect the actomyosin interaction and titin-based restorative passive force (e.g., [1013]). As previously shown [38], α 1B-adrenergic receptors are predominantly localized at the T-tubules.