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  • 1
    Electronic Resource
    Electronic Resource
    cAMP-activation of amiloride-sensitive Na+ channels from guinea-pig colon expressed in Xenopus oocytes (1996)
    Springer
    Pflügers Archiv 431 (1996), S. 913-922 
    Details
    ISSN: 1432-2013
    Keywords: Key wordsXenopus oocytes ; Guinea-pig colon ; Na+ channel ; Single-channel analysis ; Amiloride ; Benzamil ; cAMP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Guinea-pig distal colonic mRNA injection into Xenopus laevis oocytes resulted in expression of functional active epithelial Na+ channels in the oocyte plasma membrane. Poly(A)+ RNA was extracted from distal colonic mucosa of animals fed either a high-salt (HS) or a low-salt (LS) diet. The electrophysiological properties of the expressed amiloride-sensitive Na+ conductances were investigated by conventional two-electrode voltage-clamp and patch-clamp measurements. Injection of poly(A)+ RNA from HS-fed animals [from hereon referred to as HS-poly(A)+ RNA] into oocytes induced the expression of amiloride-sensitive Na+ conductances. On the other hand, oocytes injected with poly(A)+ RNA from LS-fed animals [LS-poly(A)+ RNA] expressed a markedly larger amount of amiloride-blockable Na+ conductances. LS-poly(A)+ RNA-induced conductances were completely inhibitable by amiloride with a K i of 77 nM, and were also blocked by benzamil with a K i of 1.8 nM. 5-(N-Ethyl-N-isopropyl)-amiloride (EIPA), even in high doses (25 μM), had no detectable effect on the Na+ conductances. Expressed amiloride-sensitive Na+ channels could be further activated by cAMP leading to nearly doubled clamp currents. When Na+ was replaced by K+, amiloride (1 μM) showed no effect on the clamp current. Single-channel analysis revealed slow gating behaviour, open probabilities (P o) between 0.4 and 0.9, and slope conductances of 3.8 pS for Na+ and 5.6 pS for Li+. The expressed channels showed to be highly selective for Na+ over K+ with a permeability ratio P Na/P K 〉 20. Amiloride (500 nM) reduced channel P o to values 〈 0.05. All these features make the guinea-pig distal colon of LS-fed animals an interesting mRNA source for the expression of highly amiloride-sensitive Na+ channels in Xenopus oocytes, which could provide new insights in the regulatory mechanism of these channels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050085
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  • 2
    Electronic Resource
    Electronic Resource
    Selection in segregating generations of autogamous species II. Response to selection in two stages (1984)
    Springer
    Euphytica 33 (1984), S. 447-454 
    Details
    ISSN: 1573-5060
    Keywords: Self-fertilizing crops ; quantitative genetics ; selection index ; size of cross progenies ; combined selection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary In autogamous species the optimum number of families is calculated for a selection program in two stages conducted in segregating generations. The influence of epistasis is not large. In case of much epistasis the number of families at the first stage must be reduced. In comparison with selection in later generations the second stage is relatively important. Two stage selection is more efficient than combined selection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00021144
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  • 3
    Electronic Resource
    Electronic Resource
    Selection in segregating generations of autogamous species. I. Selection response for combined selection (1982)
    Springer
    Euphytica 31 (1982), S. 493-502 
    Details
    ISSN: 1573-5060
    Keywords: Quantitative genetics ; selection index ; size of cross progenies ; pedigree method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The response to selection is determined by the genetic and nongenetic variance, the selection intensity, and the size of the experiments. If, in pure line breeding, selection starts in segregating generations, the gain depends on the relation of additive to epistatic variance. The gain can be increased if an index is constructed using the information from relatives. From animal breeding this kind of selection is known as combined selection. In this paper the optimal number of families and subfamilies is determined that will maximise the selection response by combined selection for a fixed total size of experiments. The composition of the genetic variance has a imited influence on the optimal size of the progenies. If epistatic variance is important, then the number of F2 families has to be reduced and the number of F3 families and F4 families must be increased. The same is true if the nongenetic variance is increased.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00021668
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  • 4
    Electronic Resource
    Electronic Resource
    Number and size of cross progenies from a constant total number of plants manageable in a breeding program (1979)
    Springer
    Euphytica 28 (1979), S. 453-456 
    Details
    ISSN: 1573-5060
    Keywords: Self fertilizing crops ; vegetatively propagated crops ; number of crosses ; size of cross progenies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary This short paper discusses the optimum number of crosses and size of progenies for a given total population size to minimize the risk of not finding any favourable genotype in the breeding material. It is shown that the number of crosses must generally be as large as possible. In special situations it may be advantageous to include also less promising crosses instead of enlarging the progenies of more promising crosses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00056604
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  • 5
    Electronic Resource
    Electronic Resource
    Ion transport across leech integument (1993)
    Springer
    Journal of comparative physiology 163 (1993), S. 153-159 
    Details
    ISSN: 1432-136X
    Keywords: Na+ channels ; Amiloride ; Benzamil ; Noise analysis ; Leech, Hirudo medicinalis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The dorsal skin of the leech Hirudo medicinalis was used for electrophysiological measurements performed in Ussing chambers. The leech skin is a tight epithelium (transepithelial resistance = 10.5±0.5 kΩ· cm-2) with an initial short-circuit current of 29.0±2.9 μA·cm-2. Removal of Na+ from the apical bath medium reduced short-circuit current about 55%. Ouabain (50μmol·l-1) added to the basolateral solution, depressed the short-circuit current completely. The Na+ current saturated at a concentration of 90 mmol Na+·l-1 in the apical solution (K M=11.2±1.8 mmol·l-1). Amiloride (100 μmol·l-1) on the apical side inhibited ca. 40% of the Na+ current and indicated the presence of Na+ channels. The dependence of Na+ current on the amiloride concentration followed Michaclis-Menten kinetics (K i=2.9±0.4 μmol·l-1). The amiloride analogue benzamil had a higher affinity to the Na+ channel (K i=0.7±0.2 μmol·l-1). Thus, Na+ channels in leech integument are less sensitive to amiloride than channels known from vertebrate epithelia. With 20 mmol Na+·l-1 in the mucosal solution the tissue showed an optimum amiloride-inhibitable current, and the amiloride-sensitive current under this condition was 86.8±2.3% of total short-circuit current. Higher Na+ concentrations lead to a decrease in amiloride-blockade short-circuit current. Sitmulation of the tissue with cyclic adenosine monophosphate (100 μmol·l-1) and isobutylmethylxanthine (1 mmol·l-1) nearly doubled short-circuit current and increased amiloride-sensitive Na+ currents by 50%. By current fluctuation analysis we estimated single Na+ channel current (2.7±0.9 pA) and Na+ channel density (3.6±0.6 channels·μm-2) under control conditions. After cyclic adenosine monophosphate stimulation Na+ channel density increased to 5.4±1.1 channels·μm-2, whereas single Na+ channel current showed no significant change (1.9±0.2 pA). These data present a detailed investigation of an invertebrate epithelial Na+ channel, and show the similarities and differences to vertebrate Na+ channels. Whereas the channel properties are different from the classical vertebrate Na+ channel, the regulation by cyclic adenosine monophosphate seems similar. Stimulation of Na+ uptake by cyclic adenosine monophosphate is mediated by an increasing number of Na+ channels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00263601
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