As the dynamic properties of cardiac sarcomeres are markedly changed in response to a length change of even ~0.1 μm, it is imperative to quantitatively measure sarcomere length (SL). Here we show a novel system using quantum dots (QDs) that enables a real-time measurement of the length of a single sarcomere in cardiomyocytes. First, QDs were conjugated with anti-α-actinin antibody, and applied to the sarcomeric Z-discs in isolated skinned cardiomyocytes of the rat. At partial activation, spontaneous sarcomeric oscillations (SPOC) occurred, and QDs provided a quantitative measurement of the length of a single sarcomere over the broad range (i.e., from ~1.6 to ~2.3 μm). It was found that the SPOC amplitude was inversely related to SL, but the period showed no correlation with SL. We then treated intact cardiomyocytes with the mixture of the antibody-QDs and FuGENE®HD, and visualized the movement of the Z-lines/T-tubules. At a low frequency of 1 Hz, the cycle of the motion of a single sarcomere consisted of fast shortening followed by slow relengthening. However, an increase in stimulation frequency to 3 - 5 Hz caused a phase shift of shortening and relengthening due to acceleration of relengthening, and the waveform became similar to that observed during SPOC. Finally, the anti-α-actinin antibody-QDs were transfected from the surface of the beating heart in vivo. The striated patterns with ~1.96 μm intervals were observed after perfusion under fluorescence microscopy, and an electron microscopic observation confirmed the presence of QDs in and around the T-tubules and Z-discs, but primarily in the T-tubules, within the first layer of cardiomyocytes of the left ventricular wall. Therefore, QDs are a useful tool to quantitatively analyze the movement of single sarcomeres in cardiomyocytes, under various experimental settings.
- cardiac muscle
- molecular imaging
- Copyright © 2011, American Journal of Physiology - Cell Physiology