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The neuronal growth cone appears at the tip of dendrites and axons where it plays an important role in the navigation of dendritic and axonal growth. Growth cones are rich [...]

Actin bundles play an important role in many kinds of cell activities, such as muscle contraction, cytoplasmic streaming, cell migration, and acrosomal reaction. Using our modified polarized light microscope (1), [...]

It is of paramount importance to investigate the relation between the time-dependent change in intracellular Ca[sup 2+] concentration ([Ca[sup 2+]][sub i]) (Ca[sup 2+] transients) and the mechanical activity of isolated single myocytes to understand the regulatory mechanisms of heart function. However, because of technical difficulties in performing mechanical measurements with single myocytes, the simultaneous recording of Ca[sup 2+] transients and mechanical activity has mainly been performed with multicellular cardiac preparations that give conflicting results concerning Ca[sup 2+] transients during isometric twitches and during twitches with unloaded shortening. In the present study, we coupled intracellular Ca[sup 2+] measurement optics with a force measurement system using carbon fibers to examine the relation between Ca[sup 2+] transients and the mechanical activity of rat single ventricular myocytes over a wide range of load. To minimize the possible load dependence of sarcoplasmic reticulum Ca[sup 2+] loading, contraction mode was switched at every twitch from unloaded shortening to isometric contraction. During a twitch with unloaded shortening, the Ca[sup 2+] transients exhibited a higher peak and a higher rate of decay than transients during an isometric twitch. Similarly, when we changed the contraction mode in every pair of twitches, Ca[sup 2+] transients were dependent only on the mode of contraction. Mechanical uncoupling with 2,3-butanedione monoxime abolished this dependence on the mode of contraction. Our results suggest that Ca[sup 2+] transients reflect the affinity of troponin C for Ca[sup 2+], which is influenced by the change in strain on the thin filament but not by the length change per se. [ABSTRACT FROM AUTHOR]

Determines the effects of calcium and drugs that affect the liberation of calcium from the sarcoplasmic reticulum of the skeletal muscle fiber on the contractile activity of Vorticella. Effect of calcium concentration on triton-extracted specimens; Injection of calcium buffer into the cell body of living Vorticella. Effects of drugs on degree of contraction.

Although quantitative analysis of biological images demands precise extraction of specific organelles or cells, it remains challenging in broad-field grayscale images, where traditional thresholding methods have been hampered due to complex image features. Nevertheless, rapidly growing artificial intelligence technology is overcoming obstacles. We previously reported the fine-tuned apodized phase-contrast microscopy system to capture high-resolution, label-free images of organelle dynamics in unstained living cells (Shimasaki, K. et al. (2024). Cell Struct. Funct., 49: 21-29). We here showed machine learning-based segmentation models for subcellular targeted objects in phase-contrast images using fluorescent markers as origins of ground truth masks. This method enables accurate segmentation of organelles in high-resolution phase-contrast images, providing a practical framework for studying cellular dynamics in unstained living cells.Key words: label-free imaging, organelle dynamics, apodized phase contrast, deep learning-based segmentation.

It is of paramount importance to investigate the relation between the time-dependent change in intracellular Ca2+ concentration ([Ca2+]i) (Ca2+ transients) and the mechanical activity of isolated single myocytes to understand the regulatory mechanisms of heart function. However, because of technical difficulties in performing mechanical measurements with single myocytes, the simultaneous recording of Ca2+ transients and mechanical activity has mainly been performed with multicellular cardiac preparations that give conflicting results concerning Ca2+ transients during isometric twitches and during twitches with unloaded shortening. In the present study, we coupled intracellular Ca2+ measurement optics with a force measurement system using carbon fibers to examine the relation between Ca2+ transients and the mechanical activity of rat single ventricular myocytes over a wide range of load. To minimize the possible load dependence of sarcoplasmic reticulum Ca2+ loading, contraction mode was switched at every twitch from unloaded shortening to isometric contraction. During a twitch with unloaded shortening, the Ca2+ transients exhibited a higher peak and a higher rate of decay than transients during an isometric twitch. Similarly, when we changed the contraction mode in every pair of twitches, Ca2+ transients were dependent only on the mode of contraction. Mechanical uncoupling with 2,3-butanedione monoxime abolished this dependence on the mode of contraction. Our results suggest that Ca2+ transients reflect the affinity of troponin C for Ca2+, which is influenced by the change in strain on the thin filament but not by the length change per se.