title: Real-time measurement of the length of a single sarcomere in rat ventricular myocytes: a novel analysis with quantum dots.
abstract: 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 disks 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 ∼1.7 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 disks, 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.
authors.affiliation: Department of Cell Physiology, The Jikei University School of Medicine, Tokyo, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Serizawa
authors.forename: Takako
authors.initials: T
authors.lastname: Terui
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Kagemoto
authors.forename: Akari
authors.initials: A
authors.lastname: Mizuno
authors.forename: Togo
authors.initials: T
authors.lastname: Shimozawa
authors.forename: Fuyu
authors.initials: F
authors.lastname: Kobirumaki
authors.forename: Shin'ichi
authors.initials: S
authors.lastname: Ishiwata
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kurihara
authors.forename: Norio
authors.initials: N
authors.lastname: Fukuda
mesh_terms: D000818:Animals; D008297:Male; D009200:Myocardial Contraction / Q000502:physiology; D032383:Myocytes, Cardiac / Q000502:physiology* / Q000648:ultrastructure; D045663:Quantum Dots; D051381:Rats; D017208:Rats, Wistar; D012518:Sarcomeres / Q000502:physiology* / Q000648:ultrastructure