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Interpreting photoactivated fluorescence microscopy measurements of steady-state actin dynamics. 总被引:1,自引:0,他引:1
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A continuum model describing the steady-state actin dynamics of the cytoskeleton of living cells has been developed to aid in the interpretation of photoactivated fluorescence experiments. In a simplified cell geometry, the model assumes uniform concentrations of cytosolic and cytoskeletal actin throughout the cell and no net growth of either pool. The spatiotemporal evolution of the fluorescent actin population is described by a system of two coupled linear partial-differential equations. An analytical solution is found using a Fourier-Laplace transform and important limiting cases relevant to the design of experiments are discussed. The results demonstrate that, despite being a complex function of the parameters, the fluorescence decay in photoactivated fluorescence experiments has a biphasic behavior featuring a short-term decay controlled by monomer diffusion and a long-term decay governed by the monomer exchange rate between the polymerized and unpolymerized actin pools. This biphasic behavior suggests a convenient mechanism for extracting the parameters governing the fluorescence decay from data records. These parameters include the actin monomer diffusion coefficient, filament turnover rate, and ratio of polymerized to unpolymerized actin. 相似文献
23.
Transplantation of pronuclei between one-cell-stage embryos was used to construct diploid mouse embryos with two female pronuclei ( biparental gynogenones ) or two male pronuclei ( biparental androgenones ). The ability of these embryos to develop to term was compared with control nuclear-transplant embryos in which the male or the female pronucleus was replaced with an isoparental pronucleus from another embryo. The results show that diploid biparental gynogenetic and androgenetic embryos do not complete normal embryogenesis, whereas control nuclear transplant embryos do. We conclude that the maternal and paternal contributions to the embryonic genome in mammals are not equivalent and that a diploid genome derived from only one of the two parental sexes is incapable of supporting complete embryogenesis. 相似文献
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Effects of low-chloride solutions on action potentials of sheep cadiac purkinje fibers 总被引:2,自引:0,他引:2
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The rapid repolarization during phase 1 of the action potential of sheep cardiac purkinje fibers has been attributed to a time- and voltage-dependent chloride current. In part, this conclusion was based on experiments that showed a substantial slowing of phase 1 when larger, presumably impermeant, anions were substituted for chloride in tyrode’s solution. We have re- examined the electrical effects of low-chloride solutions. We recorded action potentials of sheep cardiac purkinje fibers in normal tyrode’s solution and in low-chloride solutions made by substituting sodium propionate, acetylglycinate, methylsulfate, or methanesulfonate for the NaCl of Tyrode’s solution. Total calcium was adjusted to keep calcium ion activity of test solutions equal to that of control solutions. Propionate gave qualitatively variable results in preliminary experiments; it was not tested further. Low-chloride solutions made with the other anions gave much more consistent results: phase 1 and the notch that often occurs between phases 1 and 2 were usually unaffected, and the action potential duration usually increased. The only apparent change in the resting potential was a transient 3-6 mV depolarization when low-chloride solution was first admitted to the chamber, and a symmetrical transient hyperpolarization when chloride was returned to normal. If a time- and voltage-dependent chloride current exists in sheep cardiac purkinje fibers, our results suggest that it plays little role in generating phase 1 of the action potential. 相似文献
26.
James P. Kutney John Balsevich Robert Carruthers Arie Markus Michael J. McGrath Robert N. Young Brian R. Worth 《Bioorganic chemistry》1978,7(3):289-302
Syntheses of the C8 and C10 olefinic units cis- and trans-5-ethyl-1-iodo-hex-4-enes and cis- and trans-7-ethyl-3-iodo-oct-6-enes are described. The Wittig coupling of such units with derivatives of α- and β-thujaketonic acids to give analogs of insect juvenile hormones is discussed. 相似文献
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Tryptic peptide sequences from the 22 kDa polypeptide of tomato LHCI were used to construct a probe for gene cloning. The two genes cloned, cab11 and cab12, encode proteins of 251 and 250 residues that are 88% identical in overall amino acid sequence and 93% identical in the deduced mature protein. Each gene is present in a single copy per haploid genome; cab11 on chromosome 3 and cab12 on chromosome 6, and each has 2 introns located in similar positions to introns in other members of the Chl a/b-binding (CAB) protein gene family. Comparison of the amino acid sequences of LHCI, LHCII, CP29 and CP24 polypeptides confirms that all CABs share two regions of very high similarity which include the first and third transmembrane helices and the stroma-exposed sequences preceding them. However, near the N-terminus and between the conserved regions, the LHCI polypeptides have sequence motifs which appear to be PSI-specific. 相似文献
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The volumetric response of oocytes during rapid alterations of the extracellular osmotic environment were recorded using video microscopy. From these observations, the kinetics of water loss for human and mouse oocytes were determined over the temperature range 37 to 10 degrees C, including 37, 30, 20, and 10 degrees C. The changes in diameter of oocytes were measured over a 5-min period and a computer model was used to derive values for membrane water permeability (Lp) and inactive volume (Vb) and to compare the experimental data to the predicted values. The results for the mouse oocyte Lp were comparable to values determined by other methods. However the human data, for both failed-to-fertilize and fresh oocytes, have a wide range of values with large standard deviations. The Lp values at the various temperatures were used to calculate the Arrhenius activation energy (Ea). An Ea value of 9.48 kcal/mol was found for the fresh mouse oocyte, whereas the activation energy for human oocytes was extremely low, 3.73 kcal/mol for fresh oocytes and 1.93 kcal/mol for failed-to-fertilize oocytes. 相似文献