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It is of paramount importance to investigate the relation between the time-dependent change in intracellular [Ca.sup.2+] concentration ([[Ca.sup.2+]]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. calcium ion transients; load dependence; carbon fibers

The rotational spectra of the CrF and CrCl radicals in the X 6Σ+ state were observed by employing a Fourier transform microwave spectrometer. The CrF and CrCl radicals were generated by the reaction of laser-ablated Cr with F2 and Cl2, respectively, diluted in Ar. A chromium rod made of chromium powder pasted with epoxy resin was ablated by a Nd:YAG laser. Rotational transitions were measured in the region between 8 and 26 GHz. Several hyperfine constants due to the halogen nuclei were determined by a least-squares analysis. The electronic properties of CrF and CrCl were derived from their hyperfine constants and were compared with those of other 3d transition metal monohalides: TiF, MnF, FeF, CoF, NiF, and FeCl. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

To facilitate cardiac muscle research, we developed a novel method by which the force and length of a single ventricular myocyte can be recorded with a pair of carbon graphite fibers attached firmly to both ends. One fiber was stiff, whereas the other fiber was compliant to allow the recording of force and shortening during twitch contractions. The image of the compliant carbon fiber was projected onto a pair of photodiodes, and their output was fed to a piezoelectric transducer after variable amplifications to alter the effective compliance of the carbon fiber. Thus contraction of the myocyte was induced under virtually isometric conditions as well as under auxotonic conditions. We obtained a bell-shaped relation between the compliance under an auxotonic load and the work output of the myocyte, which was directly related to myocyte performance in the heart. Because it is easy to attach myocytes to the experimental apparatus, the present method would allow us to study cardiac muscle mechanics at the cellular and molecular levels. carbon graphite fiber; isometric contraction

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), [...]