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Selected AbstractsProtein kinase A modulates A-type potassium currents of larval zebrafish (Danio rerio) white muscle fibresACTA PHYSIOLOGICA, Issue 2 2009C. A. Coutts Abstract Aims:, Potassium (K+) channels are involved in regulating cell excitability and action potential shape. To our knowledge, very little is known about the modulation of A-type K+ currents in skeletal muscle fibres. Therefore, we sought to determine whether K+ currents of zebrafish white skeletal muscle were modulated by protein kinase A (PKA). Methods:, Pharmacology and whole-cell patch clamp were used to examine A-type K+ currents and action potentials associated with zebrafish white skeletal muscle fibres. Results:, Activation of PKA by a combination of forskolin + 3-isobutyl-1-methylxanthine (Fsk + IBMX) decreased the peak current density by ,60% and altered the inactivation kinetics of A-type K+ currents. The specific PKA inhibitor H-89 partially blocked the Fsk + IBMX-induced reduction in peak current density, but had no effect on the change in decay kinetics. Fsk + IBMX treatment did not shift the activation curve, but it significantly reduced the slope factor of activation. Activation of PKA by Fsk + IBMX resulted in a negative shift in the V50 of inactivation. H-89 prevented all Fsk + IBMX-induced changes in the steady-state properties of K+ currents. Application of Fsk + IBMX increased action potential amplitude, but had no significant effect on action potential threshold, half width or recovery rate, when fibres were depolarized with single pulses, paired pulses or with high-frequency stimuli. Conclusion:, PKA modulates the A-type K+ current in zebrafish skeletal muscle and affects action potential properties. Our results provide new insights into the role of A-type K+ channels in muscle physiology. [source] Development of ionic currents of zebrafish slow and fast skeletal muscle fibersDEVELOPMENTAL NEUROBIOLOGY, Issue 3 2006Christopher A. Coutts Abstract Voltage-gated Na+ and K+ channels play key roles in the excitability of skeletal muscle fibers. In this study we investigated the steady-state and kinetic properties of voltage-gated Na+ and K+ currents of slow and fast skeletal muscle fibers in zebrafish ranging in age from 1 day postfertilization (dpf) to 4,6 dpf. The inner white (fast) fibers possess an A-type inactivating K+ current that increases in peak current density and accelerates its rise and decay times during development. As the muscle matured, the V50s of activation and inactivation of the A-type current became more depolarized, and then hyperpolarized again in older animals. The activation kinetics of the delayed outward K+ current in red (slow) fibers accelerated within the first week of development. The tail currents of the outward K+ currents were too small to allow an accurate determination of the V50s of activation. Red fibers did not show any evidence of inward Na+ currents; however, white fibers expressed Na+ currents that increased their peak current density, accelerated their inactivation kinetics, and hyperpolarized their V50 of inactivation during development. The action potentials of white fibers exhibited significant changes in the threshold voltage and the half width. These findings indicate that there are significant differences in the ionic current profiles between the red and white fibers and that a number of changes occur in the steady-state and kinetic properties of Na+ and K+ currents of developing zebrafish skeletal muscle fibers, with the most dramatic changes occurring around the end of the first day following egg fertilization. © 2005 Wiley Periodicals, Inc. J Neurobiol, 2006 [source] The assembly factor P17 from bacteriophage PRD1 interacts with positively charged lipid membranesFEBS JOURNAL, Issue 20 2000Juha M. Holopainen The interactions of the assembly factor P17 of bacteriophage PRD1 with liposomes were investigated by static light scattering, fluorescence spectroscopy, and differential scanning calorimetry. Our data show that P17 binds to positively charged large unilamellar vesicles composed of the zwitterionic 1-palmitoyl-2-oleoyl-phosphatidylcholine and sphingosine, whereas only a weak interaction is evident for 1-palmitoyl-2-oleoyl-phosphatidylcholine vesicles. P17 does not bind to negatively charged membranes composed of 1-palmitoyl-2-oleoyl-phosphatidylglycerol and 1-palmitoyl-2-oleoyl-phosphatidylcholine. Our differential scanning calorimetry results reveal that P17 slightly perturbs the phase behaviour of neutral phosphatidylcholine and negatively charged multilamellar vesicles. In contrast, the phase transition temperature of positively charged dimyristoylphosphatidylcholine/sphingosine multilamellar vesicles (molar ratio 9 : 1, respectively) is increased by approximately 2.4 °C and the half width of the enthalpy peak broadened from 1.9 to 5.6 °C in the presence of P17 (protein : lipid molar ratio 1 : 47). Moreover, the enthalpy peak is asymmetrical, suggesting that lipid phase separation is induced by P17. Based on the far-UV CD spectra, the ,-helicity of P17 increases upon binding to positively charged micelles composed of Triton X-100 and sphingosine. We propose that P17 can interact with positively charged lipid membranes and that this binding induces a structural change on P17 to a more tightly packed and ordered structure. [source] MarqX: a new program for whole-powder-pattern fittingJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2000Y. H. Dong MarqX is a computer program for the modelling of powder diffraction data. It can be used for an unconstrained profile fitting (pattern decomposition, PD) or constrained modelling of the whole powder pattern (Pawley method, PM), for single- as well as multiple-phase samples. The program output includes: lattice parameters or peak positions (for PM and PD, respectively), width and shape of the diffraction peak (in terms of half width at half-maximum and mixing parameter of a pseudo-Voigt function), corrected for the instrumental broadening component, intensity, peak area and profile asymmetry. In addition, errors on the goniometer zero and shift in sample position with respect to the goniometric axis can also be modelled, together with distance and relative intensity of the spectral components of the X-ray beam (e.g.K,1 and K,2). Specific output files are provided for line-profile analysis, including the Williamson,Hall plot and Warren,Averbach method. [source] The effects of nebula surface density profile and giant-planet eccentricities on planetary accretion in the inner solar systemMETEORITICS & PLANETARY SCIENCE, Issue 11 2002J. E. CHAMBERS Two surface density profiles are examined: a decaying profile with , , 1/a, where a is orbital semi-major axis, and a peaked profile in which , increases for a < 2 AU and decreases for a > 2 AU. The peaked profiles are generated by models of coagulation in an initially hot nebula. Models with initial ej,s = 0.05 (the current value) and 0.1 are considered. Simulations using the decaying profile with ej,s = 0.1 produce systems most like the observed planets in terms of mass-weighted mean a and the absence of a planet in the asteroid belt. Simulations with doubled , produce planets roughly twice as massive as the nominal case. Most initial embryos are removed in each simulation via ejection from the solar system or collision with the Sun. The asteroid belt is almost entirely cleared on a timescale of 10,100 Ma that depends sensitively on ej,s. Most initial mass with a < 2 AU survives, with the degree of mass loss increasing with a. Mass loss from the terrestrial region occurs on a timescale that is long compared to the mass loss time for the asteroid belt. Substantial radial mixing of material occurs in all simulations, but is greater in simulations with initital ej,s = 0.05. The degree of mixing is equivalent to a feeding zone of half width 1.5 and 0.9 AU for an Earth mass planet at 1 AU for the cases ej,s = 0.05 and 0.1, respectively. In simulations with ej,s = 0.05, roughly one-third and 5,10% of the mass contained in final terrestrial planets originated in the region a > 2.5 AU for the decaying and peaked profiles, respectively. In the case ej,s = 0.1, the median mass accreted from a > 2.5 AU is zero for both profiles. [source] | |||||||||||||