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  • Cation π-electron interaction  (1)
  • Cell lineage  (1)
  • Chick embryo  (1)
  • 1
    Electronic Resource
    Electronic Resource
    The selectivity of different external binding sites for quaternary ammonium ions in cloned potassium channels (1995)
    Springer
    Pflügers Archiv 430 (1995), S. 672-681 
    Details
    ISSN: 1432-2013
    Keywords: Outward rectifier ; Potassium channels ; Tetraethylammonium ; Tetrapentylammonium ; Quaternary ammonium ion ; Cation π-electron interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Tetraethylammonium (TEA) is thought to be the most effective quaternary ammonium (QA) ion blocker at the external site of K+ channels, and small changes to the TEA ion reduce its potency. To examine the properties of the external QA receptor, we applied a variety of QA ions to excised patches from human embryonic kidney cells or Xenopus oocytes transfected with the delayed rectifying K+ channels Kv 2.1 and Kv 3.1. In outside-out patches of Kv 3.1, the relative potencies were TEA 〉 tetrapropylammonium (TPA) 〉 tetrabutylammonium (TBA). In contrast to Kv 3.1, the relative potencies in Kv 2.1 were TBA 〉 TEA 〉 TPA. In Kv 3.1 and Kv 2.1, external tetrapentylammonium (TPeA) blocked K+ currents in a fast, reversible and, in contrast to TEA, time-dependent manner. The external binding of TPeA appeared to be voltage independent, unlike the effects of TPeA applied to inside-out patches. External n-alkyl-triethylammonium compounds (C8, C10 chain length) had a lower affinity than TEA in Kv 3.1, but a higher affinity than TEA in Kv 2.1. In Kv 3.1, the decrease in QA affinity was large when one or two methyl groups were substituted for ethyl groups in TEA, but minor when propyl groups replaced ethyl groups. Changes in the free energy of binding could be correlated to changes in the free energy of hydration of TEA derivatives calculated by continuum methodology. These results reveal a substantial hydrophobic component of external QA ion binding to Kv 2.1, and to a lesser degree to Kv 3.1, in addition to the generally accepted electrostatic interactions. The chain length of hydrophobic TEA derivatives affects the affinity for the hydrophobic binding site, whereas the hydropathy of QA ions determines the electrostatic interaction energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00386161
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Mapping the origin of the avian enteric nervous system with a retroviral marker (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Developmental Dynamics 201 (1994), S. 236-244 
    Details
    ISSN: 1058-8388
    Keywords: Spleen necrosis virus ; Enteric nervous system ; Beta-galactosidase ; Chick embryo ; Somite ; Neural crest ; lac Z gene ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The enteric nervous system is largely formed from the vagal neural crest which arises from the neuroaxis between somites 1 - 7. In order to evaluate the contribution of different regions of the vagal crest to the enteric nervous system, we marked crest cells by injecting somites 1 - 10 with a replication-defective spleen necrosis virus vector which contains the marker gene lacZ. After incubation in X-gal, lacZ-positive blue cells were found in the wall of the gut in three locations. Most were found at the peripheral edge of the developing circular muscle and within the developing submucosa, sites characteristic of developing ganglia. LacZ-positive cells in these ganglionic sites were always surrounded by HNK-1 immunostained cells, confirming their neural crest origin. LacZ-positive cells were also seen in a third location, the circular muscle layer of the esophagus and crop, and were separated from the HNK-1 positive ganglionic elements. These cells in the circular muscle are probably muscle cells derived from labeled mesodermal cells of the somite. Injection of somites 3, 4, 5, and 6 resulted in the largest percentage of preparations with lacZ-positive crest-derived cells and in the largest number of positive cells in the gut. After injection of these somites, lacZ-positive crest-derived cells were found in all regions of the gut from the proventriculus to the rectum. Very few positive crest-derived cells were found in the esophagus. Injection of somites 1, 2, and 7 resulted in a smaller percentage of preparations with positive crest-derived cells and in a smaller number of positive crest-derived cells, which were confined to the fore and midgut. The gizzard was the gut region most frequently containing labeled cells and the rectum was the region least frequently containing such cells. This suggests that the number of crest cells available for colonization of the gut decreases as the distance from the gizzard increases. We conclude that the region of the neuroaxis between somites 3 - 6 is the major source of crest cells to the gut and that crest cells from different segments of the neuroaxis do not appear to be segregated to different regions of the gut. © 1994 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aja.1002010307
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  • 3
    Electronic Resource
    Electronic Resource
    Clonal analysis of cardiac morphogenesis in the chicken embryo using a replication-defective retrovirus: I. Formation of the ventricular myocardium (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    American Journal of Anatomy 193 (1992), S. 11-23 
    Details
    ISSN: 0002-9106
    Keywords: Heart ; Development ; Cell lineage ; Myocardium ; Cardiac myocyte ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Cells of the precardiac mesoderm (stages 4-6) and dividing myocytes of early hearts (stages 10-15) were tagged with a replication-incompetent retrovirus (CXL) (Mikawa et al., 1991 b) encoding bacterial β-galactosidase (β-gal). Two protocols were used to infect the cardiogenic cells. (1) Small blocks (∼50 μm2) of anterolateral mesoderm were dissected from gastrula-stage embryos (stages 4-6) and incubated in liquid medium containing the retrovirus. After removal of CXL, the tissues were dispersed into single-cell suspensions and pressure injected into the precardiac areas of recipient embryos (stages 4-6). Such embryos were then incubated in vitro at 37°C for 2 days (New, 1968), and those embryos with beating hearts were fixed for X-gal histochemistry and paraffin serial sectioning. (2) CXL was pressure injected in ovo (embryonic stages 4-15) into cardiogenic tissues and the eggs subsequently returned to an incubator. At selected stages of development embryos or whole hearts were fixed, stained with X-gal, and serially sectioned after paraffin embedding. The first method showed that (1) cells of the precardiac mesoderm could be infected with the retrovirus, (2) the transplanted cells would differentiate into beating myocytes, and (3) β-gal expression was sufficiently high to be detected histochemically. With the second procedure we could show that (1) β-gal-tagged cells formed colonies in the myocardium, (2) the labeled cells were exclusively myocytes, (3) the number of cells per colony increased with increasing age of embryonic development, (4) the size of colonies was larger in the left than the right ventricle, (5) many of the colonies were transmural, i.e., they extended from epicardial to endocardial layers of the myocardium and generally exhibited a cone or funnel-shape with the base of the cone nearest the epicardium, (6) the orientation of myocytes within each colony changed at different layers of the myocardium, and (7) the cones contained both β-gal+ and β-gal- myocytes. DNA labeling studies with [3H]thymidine indicated that cardiogenic cells divided every 16-18 hr during the first week of development and that the CXL-labeled cells divided indistinguishably from unlabeled myocytes. Based on these observations a model for the growth of the myocardium is presented.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aja.1001930104
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    Paper (German National Licenses)
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