Resonant X-ray emission spectra of K2Ni(CN)4 x H2O at the Ni K-edge.

Resonant X-ray emission spectra were measured at the Ni K-edge for a planar low-spin nickel complex K2Ni(CN)4 x H2O. In the Ni Kbeta emission spectra, a resonant X-ray Raman scattering was observed in the pre-edge region, showing linear energy dispersion of the emitted photon with the incident photon energy. No energy loss features corresponding to the ligand-to-metal charge-transfer (LMCT) was identified. The LMCT feature is characteristic of strongly correlated systems such as NiO; therefore, the LMCT effect proves to be significantly suppressed. This is consistent considering strong covalent character between low-lying pi* ligand and metal 3d (occupied) orbitals in low-spin nickel complexes.

Magnetic circular dichroism of 3d5/2 --> 2p3/2 resonant inelastic X-ray scattering at the Ho L(III)-edge in Ho3Fe5O12.

Magnetic Circular Dichroism (MCD) of Resonant Inelastic X-ray Scattering (RIXS) of 3d(5/2) --> 2p(3/2) decay (Ho Lalpha1) was measured at the Ho L(III)-edge in Ho3Fe5O12. The MCD-RIXS, in which the intermediate state has the 2p4f(n+1) configuration due to the quadrupolar transition of 2p --> 4f, was also observed at the pre-edge region of the Ho L(III)-edge. The obvious superposition of two peaks, which comes from the high-energy off-resonant Raman scattering and the fluorescence, could be found in both the RIXS and the MCD-RIXS when the energy of the incoming X-ray was 7eV higher than the white line. The dependence of the integration of the MCD-RIXS spectra on the incident x-ray energy could roughly reproduce the MCD of X-ray absorption spectra (XAS).

Physics in muscle research.

Muscle is one of few organs whose performance can be measured by physical quantities. However, very few attempts have been made to apply theoretical physics to muscle. In this paper we will see how physical principles can be applied by taking advantage of unique properties of muscle structure. The first topic is to establish the stability conditions of sarcomere structure. The conclusions are then compared to some experimental facts. Next, we move on to the field theory fundamentals. The concept of energy density as a stress tensor is shown to be a powerful tool for the dielectric force theory to understand how proteins move under electric fields. By combining the structural stability theory and the dielectric force theory we arrive at a helical dipole array. We discuss the source of strong dipole fields and how the dipole strength could be controlled by Ca ions. The behavior of water and ions under electric fields is briefly discussed. The third topic is the mechanical stiffness of muscle in longitudinal and lateral directions. Some experimental data are shown and the physics of anisotropic stiffness is discussed. An appendix is provided to explain the pitfalls of experimenting with isolated components rather than organized structures (sarcomere).

Collagenase degrades collagen in vivo in the ischemic heart.

Previously, we showed that ischemic rat heart contains an activated procollagenase capable of degrading collagen in vitro. We now demonstrate that the collagen resident in such hearts (in vivo) also becomes degraded, producing characteristic fragments implicating the action of an activated collagenase. The evidence is the appearance of amino-terminal dansyl-Ile (+dansyl-Leu) residues in pepsin digests of re-oxygenated rat hearts and immunoblots showing 3/4 length (alphaA) fragments from type I collagen. Also, in ischemic rat myocardium, alphaA(I) and alphaA(III) fragments were detected in pepsin digests. The time periods required for the cleavage and degradation of collagen suggest the participation of a procollagenase that becomes activated. Results demonstrate for the first time that an interstitial collagenase in such hearts initiates in vivo degradation of types I and III collagens.

X-ray reflectivity at the L edges of Gd.

Preparations are underway for the experimental investigation of the roughness of magnetic interfaces in rare-earth multilayers by combining the grazing-angle X-ray scattering technique with the resonant magnetic scattering of hard X-rays. Theoretical considerations show that for small scattering angles, 2theta, the asymmetry ratio, A = [I(+) - I(-)]/[I(+) + I(-)], depends on 2theta and varies as 1/cos theta. The first step towards the goal of determining the magnetic roughness has been taken by measuring the chemical roughness (via specular reflectivity) of a Gd thin-film sample at five photon energies close to the L(3) absorption edge, which yielded the dispersion corrections, f' and f'', to the Gd atomic form factor in good agreement with the calculation of Cromer & Liberman [J. Chem. Phys. (1970), 53, 1891-1898].

Rheology of myocardium. The relation between force, velocity, sarcomere length and activation in rat cardiac muscle.

The relations between force, shortening velocity and sarcomere length (F-V-SL) during cardiac contraction, underlie Starling's Law of the Heart. F-V-SL were investigated in isolated, intact and skinned trabeculae and myocytes from rat heart. SL and V were measured with laser diffraction techniques; F was measured with a silicon strain gauge. The "ascending" F-SL relation appeared to result from both length dependent sensitivity of the contractile system to activator calcium ions and the presence of restoring forces (Fr), residing in the collagen skeleton of the muscle. Fr increased exponentially with decreasing SL below slack length to 25% of maximal twitch force (Ft) at SL = 1.60 microns. V was inversely proportional to the load and attained a maximum at zero load (Vo). Vo increased with factors that increased F: [Ca++], SL, and time during the twitch. Vo reached a maximum and remained constant (13.5 microns/s) when F attained or exceeded 50% of its maximum value. Viscous force in the passive muscle increased with V to a maximum of 4% of Ft at V = 40 microns/s. The relation between Vo and these factors could be predicted by a model of contraction in which the measured visco-elastic properties of myocardium were incorporated, while the truly unloaded maximal velocity of sarcomere shortening was assumed to be independent of the level of activation of the contractile filaments. A model of the cardiac cycle which explains the relation between Frank's and Starling's laws is presented.

An electrostatic mechanism of muscular contraction.

The electrostatic mechanism proposed in the theory of muscular contraction propounded by Iwazumi is the force produced between an electric dipole and induced dipoles on a high dielectric rod. This force is similar to one between a short bar magnet and an iron rod. The force is always attractive and unidirectional and the rod orients itself to the direction pointing to the centre of the magnet. In muscle, the active cross-projection of myosin is analogous to the bar magnet, but an electric field is created by the dipole properties of myosin which are amplified during activation by the action of calcium ions and adenosine triphosphate. The filaments of actin are analogous to the iron rod. Detailed mathematical application of this principle to the array of filaments found in muscle, with incorporation of the troponin/tropomyosin complex, yields a complete theory of muscular contraction which provides explanations for many as yet unexplained phenomena, and provides a set of specific predictions for test.

The effects of sarcomere length and Ca++ on force and velocity of shortening in cardiac muscle.

The mechanism(s) underlying the effects of varied calcium concentration and of varied sarcomere length on force development and on the velocity of shortening in cardiac muscle were investigated. Sarcomere dynamics were investigated in thin trabeculae from rat heart with laser diffraction techniques; force was measured with silicon strain gauge 10 kHz. The unloaded velocity of sarcomere shortening was measured with the use of the 'isovelocity' technique. After study of intact muscles, superfused with modified Krebs-Henseleit solution at 25 degrees C, preparations were skinned with relaxing solution containing Triton X-100 and investigated at varied free Ca++. Force increased in all intact muscles continually with sarcomere length from 1.6-2.4 microns; the relation between force and sarcomere length was convex toward the ordinate at high Ca++0 and convex toward the abscissa at low Ca++0. Similar relations between force and sarcomere length were found in skinned trabeculae. Unloaded velocity of shortening (V0) was independent of time between 50 ms and 150 ms following onset of the twitch. V0 increased, in this period with increasing sarcomere length from 1.6 to 1.9 microns from 0 to 13 micron/s; above that length the velocity was constant. V0 increased at a sarcomere length of 2.00 microns with increasing Ca++0 to a maximum at Ca++0 = 1.2 mM above which V0 remained constant though force increased by 100%. These results suggest that the force-sarcomere length relation in cardiac muscle can be explained on the basis of length dependent activation of the contractile filaments to Ca++. Whether the different responses of force and of unloaded velocity of shortening to variations in sarcomere length and in Ca++ concentration are consistent with the hypothesis that force development and unloaded velocity of shortening are controlled by different mechanisms is discussed.

Myofibril tension fluctuations and molecular mechanisms of contraction.

Recent tension fluctuation experiments that were performed on single myofibrils of cardiac and skeletal muscles established firmly that the fluctuations, if exist, must be below 0.1 ng/square root Hz. This value is about 100 times below the levels that were predicted by various models of cross-bridge mechanical cycling during isometric contraction. Similar measurements with slow stretch and shortening to promote cross-bridge cycling did not produce detectable increase of fluctuations either. Moreover, measurements of elastic transfer function using small length perturbations with white noise clearly demonstrated conduction of vibrations and increased stiffness during contraction of the myofibril; therefore, vibration attenuation within the sarcomere cannot be responsible for remarkable quietness of the tension. Electrostatic mechanism of muscle contraction advanced by Iwazumi gives physically straightforward explanations for the quietness. The ATPase cycling certainly produces fluctuations in the number of surface charges that constitute the dipole moment thus resulting in the field strength fluctuations. However, the magnitude of the fluctuations is only a small fraction of the mean strength due to large number of charges involved in the dipole. In addition, the field strength fluctuations do not couple effectively with the axial force acting on the thin filament bundle. This is due to the combined effects of three factors: 1. Three dimensional three-phase distribution of electrostatic energy density along the thin filament. This structural arrangement smoothes out the forces of three adjacent thin filaments due to complementary nature of the distribution. 2. Characteristic square mesh structure of the Z-disc results in very high shear compliance between adjacent thin filaments yet provides very low parallel compliance. 3. Electrostatic induction.

High-speed ultrasensitive instrumentation for myofibril mechanics measurements.

A novel instrument for measuring the mechanics of a single myofibril is described. The principle of the transducer operation is to attach a myofibril to a very fine wire suspended in a magnetic field. Feedback circuits pass current through the wire to maintain the length constant when the myofibril contracts. The wire position is measured optoelectronically at a resolution below 1 A. The myofibril measurement system consists of two independent transducers and is capable of resolving tension down to 0.5 ng/square root Hz and controlling the myofibril length with a 10-microseconds rise time. Optical and electronic designs of the system and calibration and adjustment procedures are described. Experimental chamber design, a flow controller, and an environmental noise cancellation scheme are also discussed.

Photoelectric caliper for noncontact measurement of vascular dynamic strain in vitro.

A photoelectric device is described for in vitro semicontinuous contact-free measurement of vascular dynamic strain. The vessel's optical image is projected onto a pair of linear photodiode arrays by use of a projection lens and a set of mirrors. Each array's video signal indicates a focused image of the vessel edge as a steep change of the light intensity. Edge location is defined as the midpoint of the intensity drop across the edge. Knowing the interdiode distance (16 micron), the location of the edge can be determined by counting the number of diodes up to the midpoint. Given both edge locations and the distance between arrays, diameter can be electronically computed. The output voltage is calibrated with a metric grid in place of the vessel and is linearly related to diameter. Resolution varies with magnification and may be on the order of 1 micron, depending on the strain amplitude and the initial unstressed vessel caliber. Frequency response is determined by the array scanning rate and is uniform well beyond the range of physiological considerations.

Some specific predictions and experiments on single myofibrillar mechanics.

The length-tension relationship of myofibrils approximately 50 sarcomeres long from skinned single atrial cells was measured. All sarcomeres were observable throughout the experiments. The tension developed at submaximal Ca2+ concentrations consistently increased with the sarcomere length.

The effect of sarcomere non-uniformity on the sarcomere length-tension relationship of skinned fibers.

It has proved difficult to activate skinned muscle fibers to produce high tension (3 kg/cm2 level) without loss of clear striations. A new method was developed which permits high tension production in skinned muscle fibers while retaining clear striations. Clear striations allow reliable measurement of the sarcomere lengths during contraction by microscopy and diffractometry. The method is to increase the Ca++ concentration of the bathing solution very gradually over a time period of 5 to 10 minutes. Once the skinned fiber is conditioned by this slow activation, subsequent contractions can be elicited by ordinary quick activations without loss of striations. When the experiments are carried out with careful controls for the uniformity of the sarcomere length distribution along the entire length of the fiber, contractions are highly repeatable. Using the new method and stringent quality control of fibers, the sarcomere length-isometric tension relationship of skinned rabbit soleus fibers was obtained. The results differ from those previously obtained by conventional activation methods in that tension increases with sarcomere length not only at low (pCa = 5.8), but also at high (pCa = 5.2), calcium concentration.

The sarcomere length-tension relation in skeletal muscle.

Tension development during isometric tetani in single fibers of frog semitendinosus muscle occurs in three phases: (a) in initial fast-rise phase; (b) a slow-rise phase; and (c) a plateau, which lasts greater than 10 s. The slow-rise phase has previously been assumed to rise out of a progressive increase of sarcomere length dispersion along the fiber (Gordon et al. 1966. J. Physiol. [Lond.]. 184:143--169;184:170--192). Consequently, the "true" tetanic tension has been considered to be the one existing before the onset of the slow-rise phase; this is obtained by extrapolating the slowly rising tension back to the start of the tetanus. In the study by Gordon et al. (1966. J. Physiol. [Lond.] 184:170--192), as well as in the present study, the relation between this extrapolated tension and sarcomere length gave the familiar linear descending limb of the length-tension relation. We tested the assumption that the slow rise of tension was due to a progressive increase in sarcomere length dispersion. During the fast rise, the slow rise, and the plateau of tension, the sarcomere length dispersion at any area along the muscle was less than 4% of the average sarcomere length. Therefore, a progressive increase of sarcomere length dispersion during contraction appears unable to account for the slow rise of tetanic tension. A sarcomere length-tension relation was constructed from the levels of tension and sarcomere length measured during the plateau. Tension was independent of sarcomere length between 1.9 and 2.6 microgram, and declined to 50% maximal at 3.4 microgram. This result is difficult to reconcile with the cross-bridge model of force generation.