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Calcium-independent contraction in lysed cell models of teleost retinal cones: activation by unregulated myosin light chain kinase or high magnesium and loss of cAMP inhibition.
The retinal cones of teleost fish contract at dawn and elongate at dusk. We have previously reported that we can selectively induce detergent-lysed models of cones to undergo either reactivated contraction or reactivated elongation, with rates and morphology comparable to those observed in vivo. Reactivated contraction is ATP dependent, activated by Ca2+, and inhibited by cAMP. In addition, reactivated cone contraction exhibits several properties that suggest that myosin phosphorylation plays a role in mediating Ca2+-activation (Porrello, K., and B. Burnside, 1984, J. Cell Biol., 98:2230-2238). We report here that lysed cone models can be induced to contract in the absence of Ca2+ by incubation with trypsin-digested, unregulated myosin light chain kinase (MLCK) obtained from smooth muscle. This observation provides further evidence that MLCK plays a role in regulating cone contraction. We also report here that lysed cone models can be induced to contract in the absence of Ca2+ by incubation with high concentrations of MgCl2 (10-20 mM). Mg2+-induced reactivated contraction is supported by inosine triphosphate (ITP) just as well as by ATP. Because ITP will not serve as a substrate for MLCK, this finding suggests that Mg2+-activation of contraction does not require myosin phosphorylation. Although Ca2+-induced contraction is completely blocked by cAMP at concentrations less than 10 microM, cAMP has no effect on cone contraction activated by unregulated MLCK or by high Mg2+ in the absence of Ca2+. Because trypsin digestion of MLCK cleaves off not only the Ca2+/calmodulin-binding site but also the site phosphorylated by cAMP-dependent protein kinase, and because Mg2+ activation of cone contraction circumvents MLCK action altogether, both these observations would be expected if cAMP inhibits reactivated cone contraction by catalyzing the phosphorylation of MLCK and thus reducing its affinity for Ca2+, as has been described for smooth muscle. Together our results suggest that in lysed cone models, myosin phosphorylation is sufficient for activating cone contraction, even in the absence of other Ca2+-mediated events, that cAMP inhibition of contraction is mediated by cAMP-dependent phosphorylation of MLCK, and that 10-20 mM Mg2+ can activate actin-myosin interaction to produce contraction in the absence of myosin phosphorylation
Recent Decisions: Labor Relations--Union Racial Discrimination Applicability of Title VII, 1964 Civil Rights Act [\u3ci\u3eVollmer v. Szabo\u3c/i\u3e, 17 Ohio Misc. 143 (N.D. Ohio 1969)]
Recent Decisions: Labor Relations--Union Racial Discrimination Applicability of Title VII, 1964 Civil Rights Act [\u3ci\u3eVollmer v. Szabo\u3c/i\u3e, 17 Ohio Misc. 143 (N.D. Ohio 1969)]
Temperature dependence in interatomic potentials and an improved potential for Ti
The process of deriving an interatomic potentials represents an attempt to
integrate out the electronic degrees of freedom from the full quantum
description of a condensed matter system. In practice it is the derivatives of
the interatomic potentials which are used in molecular dynamics, as a model for
the forces on a system. These forces should be the derivative of the free
energy of the electronic system, which includes contributions from the entropy
of the electronic states. This free energy is weakly temperature dependent, and
although this can be safely neglected in many cases there are some systems
where the electronic entropy plays a significant role. Here a method is
proposed to incorporate electronic entropy in the Sommerfeld approximation into
empirical potentials. The method is applied as a correction to an existing
potential for titanium. Thermal properties of the new model are calculated, and
a simple method for fixing the melting point and solid-solid phase transition
temperature for existing models fitted to zero temperature data is presented.Comment: CCP 201
Infrared Peak Splitting from Phonon Localization in Solid Hydrogen
We show that the isotope effect leads to a completely different spectroscopic
signal in hydrogen-deuterium mixtures, compared to pure elements that have the
same crystal structure. This is particularly true for molecular vibrations,
which are the main source of information about the structure of high-pressure
hydrogen. Mass disorder breaks translational symmetry, meaning that vibrations
are localized almost to single molecules, and are not zone-center phonons. In
mixtures, each observable IR peak corresponds to a collection of many such
molecular vibrations, which have a distribution of frequencies depending on
local environment. Furthermore discrete groups of environments cause the peaks
to split. We illustrate this issue by considering the IR spectrum of the high
pressure Phase III structure of hydrogen, recently interpreted as showing novel
phases in isotopic mixtures. We calculate the IR spectrum of hydrogen/deuterium
mixtures in the and -12 structures, showing that isotopic disorder
gives rise to mode localization of the high frequency vibrons. The local
coordination of the molecules leads to discrete IR peaks. The spread of
frequencies is strongly enhanced with pressure, such that more peaks become
resolvable at higher pressures, in agreement with the recent measurements.Comment: Final author versio
THE ART ATHLETE: A SPORTS BIOMECHANICS PERSPECTIVE
Overuse injuries are as much a problem for ‘art athletes’ (dancers and musicians and performing artists generally) as they are for those we more commonly term ‘athletes’. Lower back injuries in male ballet dancers are certainly commonplace. 3D motion analysis in combination with 3D Static Strength Predicting analysis showed that compressive forces at L5/S1 were above the National Institute of Occupational Safety and Health ‘Back Compression Design Limit’ (~ 4,500N) and shear forces were high (~ 530 N) for male dancers performing two commonly used classical lifts. A research design for the use of an opto-reflective motion analysis (Vicon) to investigate shoulder joint loading in cellists and violinists will also be presented
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