Recent advances in fluorescence nanotechnology have made it possible to observe sarcomeres within beating myocardium at nanometer precision. This article systematically reviews the development and applications of in vivo cardiac nano‑imaging in mice and rats. Conventional modalities such as echocardiography and MRI are limited to spatial resolutions of ≈ 100 µm, making it difficult to capture the ~ 100 nm sarcomere‑length changes and intracellular Ca²⁺ dynamics that underlie excitation–contraction coupling. By integrating quantum dots with high‑sensitivity EMCCD cameras, the new technology simultaneously visualizes sarcomere‑length fluctuations and Ca²⁺ transients on a beat‑to‑beat basis, enabling molecular‑scale analysis of cardiac performance in vivo.
The authors began by tracking fluorescent beads affixed to the epicardial surface to measure micrometer‑scale motions. This approach evolved into nanometer tracking of Z‑discs using fluorescent proteins fused to α‑actinin or quantum‑dot labeling. High‑temporal‑resolution recordings revealed beat‑to‑beat manifestation of the first phase of length‑dependent activation and localized asynchrony between Ca²⁺ waves and sarcomere responses, offering fresh insights into the Frank–Starling mechanism.
Applied to genetically modified and heart‑failure mouse models, the technique permits direct examination of sarcomere abnormalities and Ca²⁺ dysregulation during disease progression. Looking ahead, it is expected to serve as a platform for evaluating how drugs or gene therapies influence sarcomere mechanics in vivo, playing a pivotal role in both basic and translational research.
Article information & citation
Shimozawa T., Hirokawa E., Kobirumaki‑Shimozawa F., Oyama K., Shintani S.A., Terui T., Kushida Y., Tsukamoto S., Fujii T., Ishiwata S., Fukuda N. In vivo cardiac nano‑imaging: A new technology for high‑precision analyses of sarcomere dynamics in the heart. Progress in Biophysics and Molecular Biology, 124: 31‑40 (2017).