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Notes: [Auszug] The muscle myosins are hexomeric proteins consisting of two heavy chains and two pairs of light chains, the latter called essential (ELC) and regulatory (RLC). The light chains stabilize the long alpha helical neck of the myosin head. Their function in striated muscle, however, is only partially ...

Notes: Abstract The fact that smooth muscle exists in almost every hollow organ and is involved in a large number of disease states has led to a vast increase in smooth muscle research, covering areas from testing response to antagonists and agonists to measuring the molecular force generated by a single actin filament. Yet, the exact mechanisms regulating contractile response of smooth muscle remain unsolved. Calcium has been a central player in mediating smooth muscle contraction through binding with calmodulin, although there is evidence showing that under special circumstances smooth muscle can contract without change in intracellular Ca2+. In addition to the major regulatory pathway of Ca2+-calmodulin-mysoin light chain kinase, there are other thin filament linked regulatory mechanisms in which Ca2+-calmodulin dependent phosphorylation of calponin and caldesmon may be involved. Ca2+ sensitivity of smooth muscle contraction may vary under different situations and this has recently been recognized as an important regulatory mechanism. Examples are protein kinase C (PKC) dependent phosphorylation of myosin light chain kinase which results in partial inhibition of contraction, and activation of myosin light chain phosphatase. There is new evidence howing that not only does Ca2+ regulate contraction by regulating the interaction of contractile proteins in smooth muscle, but also that shortening of smooth muscle itself reduces intracellular Ca2+ concentration, via a negative feedback.

Notes: Abstract We have previously reported increased velocity of shortening (Vo) in the sensitized airway (0.36 1o/s, ± SE) smooth muscle compared to the control (0.26 1o/s, ± 0.017 SE) and subsequent experiments indicated this was due to increased phosphorylation of the 20 kDa myosin light chain resulting from increased total myosin light chain kinase activity. The motility assay technique described by Kron and Spudich was employed to determine whether additionally the molecular motor (actomyosin crossbridge) itself was altered in airway smooth muscle by ragweed pollen sensitization. The motility assay measures the velocity of actin filament translation by myosin molecules. The negative results of the motility assay were valuable in determining that the pathogenesis of allergic bronchospasm is not at contractile protein level but at regulatory enzyme level.

Notes: Abstract The crystal microstructure, superconductivity, and normal state transport properties of Bi1.9+x Sr1.7−x La0.4CuO6+δ(0 ≤ x ≤ 0.4) system were investigated by means of electron diffraction (ED), resistivity, and TEP. Analyses of the experimental results indicate that with the increase of Bi content, the incommensurate modulation wavelength decreases and the distortion of CuO6 octahedron enhances. Increasing Bi content decreases the carrier concentration rapidly, and induces an MI transition. The destruction of superconductivity mainly derives from two aspects: the enhancement of structural distortion due to the introduction of more Bi and the variation of the carrier concentration of the system.

Notes: Though not yet firmly established, it appears likely that the neuroendocrine system (NES) regulates airway smooth muscle function. As it is the latter which is altered in asthma, the importance of the role of the NES in this disease is clear. The fact that trnasmitters from the NE cells are released from their basal aspect, and are in close proximity to the subjacent airway smooth muscle, further indicates an interaction. The question then arises as to what are the experimental desiderata for conducting studies of the ASM. These should constitute what Sergei Sorokin has called the “Koch's postulates of airway smooth muscle research.”As human tissues from asthmatics are difficult to obtain, animal models have been developed. The requirements are that, in these animals, the allergy be IgE based, that a congenital or familial factor be operative, that a noncholinergic nonadrenergic inhibitory system be a component of the neural regulatory system, and that the antigen for immunization be of a type commonly found in human asthmatics. Ideally, evidence of clinical asthma and exercise-induced asthma and nocturnal attacks should also be present. Unfortunately, no ideal animal models exist and one cannot talk about asthmatic animals, but only of animals with allergic bronchospasm.If in vitro research is to be conducted, there are additional requirements. The tissue should be from a relevant location. The tracheal smooth muscle which has been the favorite, purely because of its convenience, is not a good model. For the early asthmatic attack, central bronchi (3-5 mm diameter) should be used. Muscle strips obtained from them should be parallelfibred and the cartilage plaques should be carefully dissected away, otherwise they contribute unwanted frictional forces when velocity is measured. Care should be taken to ensure that the epithelial cell layer is intact, as evidence indicates that it may regulate airway muscle function, though this has not been establihsed for all the animal species used in asthma research.The isolated muscle strip should be in a steady state, particularly with respect to the functional variable under study, before definitive data are collected. Most importantly, it is shortening capacity that must be studied, as this is the in vitro analogue to in vivo narrowing of airways. Isometric force development provides information about wall stiffness and is of very little relevance to the elucidation of the mechanism of bronchospasm. Furthermore, as force is measured at the plateau of the record, it only yields data relating to latch bridges which seem to play little role in narrowing the airway. Unfortunately, isometric force is the most common measurement made, purely because it is easy to carry out, while shortening is technically more difficult.The above notwithstanding, if force is the parameter being studied, its correct normalization is a very important consideration. To make comparisons, force should be converted to stress. In tissues which are more than 5 mm in length and 5 mg in weight, the required cross-sectional area can be obtained from the weight of the blotted tissue and its optimal length. For tissues smaller than this measurement errors render the approach invalid and direct measurements must be made using high performance optics. It must be remembered too that the cross-sectional area of the tissue is only appropriate when the entire tissue consists of muscle, as for example, in the case of striated muscle. In smooth muscle, muscle content may only be 25%. For this reason, tissue stress should be converted to muscle cell stress and ultimately to myosin stress, as it is the myosin crossbridges that generate the force. Estimation of muscle stress requires quantitative morphometry while myosin stress requires morphometry of immunohistochemical micrographs.Finally, in conducting studies of shortening and velocity, the nature of the loading has to be kept in mind. Such studies are usually carried out with isotonic loads as this holds that variable constant. However, in vivo the load is more likely to be elastic or visco-elastic, hence, in vitro studies should employ similar loading. In our own studies we have attempted to pay attention to the desiderata mentioned above. In bronchial smooth muscle (central airways) from 4-month-old, ragweed pollen-sensitized dogs, we have found that maximum shortening capacity and velocity are both increased while force production is normal. These changes are typical of early disease. In addition, we have found that the compliance of the muscle's so-called internal resistor is increased with sensitization. This could account for the increased shortening capacity of the muscle. We have also shown that the maximum velocity of the sensitized muscle is associated with increased myofibrillar ATPase activity. This results, not from a change in distribution in myosin heavy chain isozymes, but from increased phosphorylation of the 20,000 dalton myosin light chain that is due to an increased content of myosin light chain kinase. Our studies indicate that this increase is due to increased gene translation rather than transcription, as the content of messenger RNA for myosin light chain kinase is unchanged. © 1993 Wiley-Liss, Inc.