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  • Cell & Developmental Biology  (3)
  • 1995-1999  (1)
  • 1980-1984  (2)
  • 1930-1934
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 121 (1984), S. 235-242 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Biochemical and kinetic characteristics of the Na+-K+ exchange were studied in Paracentrotus lividus eggs. Measurement of the 86Rb uptake shows that ouabain-sensitive 86Rb uptake is dramatically stimulated within the first minute following fertilization. The Na+-K+ pump-mediated K+ entry presents a maximal rate at 8 min postfertilization and then decreases to reach a plateau within 30 min. We assess that the steep rise in cell K+ occurring at fertilization (J.P. Girard, P. Payan, C. Sardet, Exp. Cell. Res. 142:215-221, 1982) does not originate from a net entry of external K+. Measured 30 min postfertilization, the half-maximal activation by K+ of the ouabain-sensitive Na+-K+ exchange is 5-6 mM and the ouabain lC50 is 5.10-5 M. Egg cortices from unfertilized and fertilized eggs show comparable Na+-K+ ATPase activity with a 50% ouabain-sensitive fraction. Vm and Km for Na+ and K+ of the enzyme are of the same order of magnitude in cortices of unfertilized and fertilized eggs. Cortical Na+-K+ ATPase from unfertilized eggs shows a ten fold increase of activity between pH 6.7 and pH 7.7. The results strongly suggest that the plasma membrane of unfertilized eggs contains a preexisting Na+-K+ transporting system which is obligatorily stimulated at fertilization.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 121 (1984), S. 243-250 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The preceding paper (Ciapa et al., 1984) provided biochemical and kinetic characterization of the Na+-K+ exchange in Paracentrotus lividus eggs. The present work is a study of the ionic events involved in the stimulation of the Na+-K+ transporter after fertilization. Fertilization in low Na+-external medium containing amiloride (0.1 mM) suppresses the stimulation of the net efflux of H+ and 86Rb uptake. Activation of eggs with the ionophore A23187 leads to stimulation of both Na+-H+ exchange and ouabain-sensitive 86Rb influx. When eggs were activated with A23187 in artificial seawater, 86Rb uptake and 24Na influx showed similar saturable kinetics with respect to the external Na+. A23187 treatment of eggs in Na+ -free artifical seawater did not stimulate the Na+-K+ exchange until 10 mEq Na+ was added. Activation of eggs by NH4Cl (5 mM) stimulated 86Rb influx and Na+ exit; both fluxes were ouabain sensitive. Monensin increased cell Na+ of unfertilized eggs without any significant increase in intracellular pH: a condition in which 86Rb influx was not markedly stimulated. Addition of 10 mEq Na+ to unfertilized eggs in Na+-free artificial seawater stimulated 86Rb uptake but to a lower extent that did 10 mEq Na+ plus sperm. It is concluded that (1) the stimulation of the Na+-K+ pump at fertilization has an absolute requirement for the Na+-H+ exchange; (2) the alkalinization of eggs resulting from the acid efflux is a prerequisite for the enhancement of the Na+-K+ pump; (3) the amount of Na+ entering eggs at fertilization determines the intensity of the Na+-K+ exchange; (4) early events of fertilization such as exocytosis and calcium release which may be involved in the stimulation of the Na+-K+ pump must necessarily be coupled to cell alkalinization.
    Additional Material: 7 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 163 (1995), S. 179-193 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Flow-related shear stress has been shown to modulate endothelial cell structure and function including F-actin microfilament organization. Focal adhesion-associated proteins such as vinculin, talin, and specific integrins may play a role in the modulation of these cytoskeletal and morphological changes. Double-label immunofluorescence studies indicated that, in static culture, α5β1 fibronectin receptors (α5β1 FNRs) and αvβ3 vitronectin receptors (αvβ3 VNRs) were found predominantly in the peripheral regions of bovine aortic endothelial cells (BAECs) corresponding to the localization of vinculin, talin, and actin microfilament terminations. In response to shear stress, concomitant with cell elongation and the appearance of stress fibers aligned with the direction of flow, there was a prominent localization of vinculin and αvβ3 VNRs as the “upstream” end of the cells. Stress fiber terminations were clearly evident at these concentrations of focal adhesion-associated proteins. These data suggest that the upstream concentration of these proteins may direct shear stress-induced stress fiber formation and may function in the alignment of the fibers in the direction of flow. Levels of surface αvβ3 VNRs were found to decrease in response to flow, possibly reflecting the decrease in numbers of “downstream” receptors. Unlike the arrangement of vinculin and αvβ3 VNRs observed following exposure to flow, talin and α5β1 FNRs, in addition to being localized at the upstream end of the cell, were also evenly distributed throughout the rest of the cell. Surface levels of α5β1 FNRs increased in response to shear stress, perhaps providing an increased adherence of BAECs to the extracellular matrix through these receptors. These data suggest that focal adhesion-associated proteins play specific roles in the response of BAECs to shear stress. © 1995 Wiley-Liss, Inc.
    Additional Material: 10 Ill.
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