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  • Excitation-contraction coupling  (4)
  • Computational Chemistry and Molecular Modeling  (3)
  • 1
    ISSN: 1432-136X
    Keywords: Aequorin ; Calcium ; Sarcoplasmic reticulum ; Contraction ; Excitation-contraction coupling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Steps involved in excitation-contraction coupling in mammalian myocardium have been derived using a relatively limited number of animal species. However, the use of animal models for investigations into excitation-contraction coupling in normal and disease states has encompassed a wide range of animal species. We addressed the question as to whether excitation-contraction coupling as currently understood applies to intracellular calcium handling in myocardium from multiple mammalian species, amphibian, and avian myocardium. The bioluminescent calcium indicator aequorin was used to record intracellular calcium transients in both ventricular and atrial tissue. We report that in all mammalian and avian species studied the calcium transient recorded in both ventricular and atrial myocardium is monophasic and reflects calcium release and re-uptake by the sarcoplasmic reticulum. In contrast, the Ca2+ transient recorded from salamander myocardium is prolonged relative to mammalian and avian myocardium, and appears to reflect in part trans-sarcolemmal calcium entry. Only in diseased myocardium derived from human and swine myocardium was a second component detected in the calcium transient. These data indicate that sarcoplasmic reticulum calcium handling is pivotal in excitation-contraction coupling for multiple species with differing physiologies. Also, in disease states, intracellular calcium handling is often affected with resultant alterations in the time-course and/or configuration of the calcium transient.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Pflügers Archiv 395 (1982), S. 75-77 
    ISSN: 1432-2013
    Keywords: Excitation-contraction coupling ; Cell calcium ; Vascular smooth muscle ; Reversibly hyperpermeable cells ; Calcium indicators ; Aequorin ; Phenylephrine ; Angiotensin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The bioluminescent calcium indicator aequor in was successfully loaded into vascular smooth muscle cells ofAmphiuma tridactylum by either microinjection or a new method which makes the cells reversibly hyperpermeable. Both gave similar results; however, the latter method produced larger signals. Vasoconstrictors produced a sustained contraction and a light (calcium) response consisting of two component: a large transient followed by a smaller, sustained response. Electrical stimulation produced a light transient that was much briefer than the contraction. These results suggest that tension can be maintained in smooth muscle in the presence of lower calcium levels than those present during force development.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2013
    Keywords: Excitation-contraction coupling ; Cell calcium ; Mammalian cardiac muscles ; Reversibly hyperpermeable cells ; Calcium indicators ; Aequorin ; Isoproterenol ; Caffeine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The bioluminescent calcium indicator aequorin was successfully loaded into mammalian working myocardium of ferrets by a chemical procedure which makes the cells reversibly hyperpermeable through exposure to Ethylenebis-(oxyethylenenitrilo) tetraacetic acid (EGTA). After undergoing the loading procedure, developed tension at Lmax was 103±26% of the control, which indicates that the muscles regained normal function. The configurations of the aequorin signals (i.e., calcium transients) and their responses to drugs were the same as reported after microinjection of aequorin. The peak of the Ca++ transient determined by the method of fractional luminescence at 3s intervals of stimulation, 2.5mM [Ca++]o, 22.5°C was 1.1μM; this value is similar to that reported for microinjection. These results indicate that the chemical loading procedure is a useful alternative to microinjection for loading aequorin into mammalian working myocardium.
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  • 4
    ISSN: 1432-2013
    Keywords: Excitation-contraction coupling ; Cell calcium ; Cardiac muscle ; Thyroid hormone ; Aequorin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The purpose of this study was to determine the influence of thyroid hormone on tension development and the intracellular calcium transient in mammalian ventricular muscle. A hyperthyroid (H) state was induced in ferrets by subcutaneous injection ofl-thyroxine, 0.3 mg/kg daily, for 2–3 weeks. One-half of the age matched control group (C) were injected with vehicle. Aequorin was loaded into the cells of ferret papillary muscles by a chemical procedure. The muscles were stimulated at 0.33 Hz and isometric tension and the calcium transient were simultaneously recorded at 30°C. Peak isometric tension in mN/mm2 (±SD) was 15.4±7.2 and 16.2±7.9 for C (n=8) and H (n=9) respectively. The time to peak tension and time to 80% relaxation from peak of tension were reduced by 22% and 28% respectively in H compared to C. After stimulation, the calcium transient reached a maximum in 56±6 ms in C and in 47±5 ms in H. The time to 80% decay of the peak calcium transient was 95±8 ms and 68±5 ms for C and H respectively. The ratio of the aequorin luminescence at the peak of the calcium transient over the calculated maximum luminescence,L max, were compared and they were not different. At 22°C Log (L/L max) was −3.3±0.1 in C (n=4) and −3.4±0.3 in H (n=3). These results indicate that the thyroid state influences the time course of the calcium transient and are consistent with the abbreviation in the duration of contraction that is observed in the hyperthyroid state.
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  • 5
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: We compare the electrostatic potential surrounding several natural and synthetic nucleic acid bases calculated using an atom-centered multiple expansion (ACME) derived from integration of the charge distribution with that from potential-derived charges (PDCs) obtained using the CHELPG procedure. When the multipole expansions are carried out to octapoles, the root mean square (rms) error in the potential is always less than that from PDCs. Electrostatic interactions in pairs of these nucleic acid bases were also evaluated using ACMEs up to octapoles and PDCs. The electrostatic interaction energies from ACMEs were found always to be larger than those from PDCs or the total self-consistent field (SCF) interaction energy. The value of the electrostatic energy differs by as much as approximately 19 or as little as approximately 8 kJ/mol between the ACME and PDC methods. The rank ordering provided by the electrostatic models is grossly similar but differs in the ranking of systems with two and three hydrogen bonds. A rigid twist about the N—H ⃛ N axis of the pairs was examined using SCF calculations and the electrostatic models. It was found that with ACMEs the energy required for a 90-degree rotation was always higher than that found from SCF calculations. With PDCs, similar results are obtained, except with the adenine/thymine and 9-methyl-adenine/1-methyl-thymine pairs. In these instances, the barrier is about 4 kJ/mol lower than that found with SCF calculations. These results demonstrate that integration of the charge density can provide convergent multipole expansions that provide a more accurate description of the electrostatic potential than the commonly used PDC model. In addition, the description of electrostatic interactions during twisting of AT and mAmT given by this model is shown to be somewhat anomalous. © 1995 by John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Molecular orbital calculations using the 3-21G basis set have been performed for iso-butylene (IB; 2-methyl-1-propene), difluoro-iso-butylene (DFIB; 1,1-difluoro-2-methyl-1-propene), hexafluoro-iso-butylene (HFIB; 3,3,3-trifluoro-2-(trifluoromethyl)-1-propene), and perfluoro-iso-butylene (PFIB; 1,1,3,3,3-pentafluoro-2-(trifluoromethyl)-1-propene). The effects of fluorine substitution were studied by comparison of several calculated quantities of the fluorinated compounds with those of IB. Through an analysis of the computed electron density distributions, it is suggested that a vinylic fluorine acts as a π acceptor, by electron transfer into the C—F bond, and a π repeller, by polarization of the adjacent π electrons. An allylic fluorine acts as a π attractor through electrostatic effects, although in HFIB a minor contribution from hyperconjugation was evident. Finally, electrostatic potentials for the molecules were calculated. These show that fluorine substitution has large effects on the electrostatic potential associated with the π electrons. These effects change the sign of the calculated electrostatic potential in the plane containing the π bond to such an extent that PFIB is quite susceptible to nucleophilic attack.
    Additional Material: 8 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 8 (1987), S. 499-509 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Accurate and efficient integration of the electron density function over arbitrary regions has been previously achieved by exploiting a separation of variables. Recently, a computer program has been written that calculates ρ, \documentclass{article}\pagestyle{empty}\begin{document}$ \buildrel{\rightharpoonup}\over{\nabla} $\end{document}ρ, and ∇2ρ in an expeditious fashion, taking advantage of the separation of variables in the electron density function. Accurate integrations of ∇2ρ over arbitrary regions can also be accomplished. The structure of the program is suited especially to vector processors. As a result of the efficiencies of these programs, functions of the electron density, such as the density itself, the surrounding electrostatic potential, ∇ρ, and ∇2ρ have been calculated in three dimensions. Results of calculations for nitrated cubanes are presented illustrating how the effects of the nitro groups are manifested in the electron density and associated properties.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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