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  • 1
    Electronic Resource
    Electronic Resource
    Special Topic: Polarity of Epithelial Cells: Intracellular Sorting and Insertion (1989)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physiology 51 (1989), S. 727-728 
    Details
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.ph.51.030189.003455
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  • 2
    Electronic Resource
    Electronic Resource
    Basolateral membrane potential of a tight epithelium: Ionic diffusion and electrogenic pumps (1978)
    Springer
    The journal of membrane biology 41 (1978), S. 117-148 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The contribution of specific ions to the conductance and potential of the basolateral membrane of the rabbit urinary bladder has been studied with both conventional and ion-specific microelectrode techniques. In addition, the possibility of an electrogenic active transport process located at the basolateral membrane was studied using the polyene antibiotic nystatin. The effect of ion-specific microelectrode impalement damage on intracellular ion activities was examined and a criterion set for acceptance or rejection of intracellular activity measurements. Using this criterion, we found (K+)=72mm and (Cl−)=15.8mm. Cl− but not K+ was in electrochemical equilibrium across the basolateral membrane. The selective permeability of the basolateral membrane was measured using microelectrodes, and the data analyzed using the Goldman, Hodgkin-Katz equation. The sodium to potassium permeability ratio (P Na/P K) was 0.044, and the chloride to potassium permeability ratio (P Cl/P K) was 1.17. Since K+ was not in electrochemical equilibrium, intracellular (K+) is maintained by active metabolic processes, and the basolateral membrane potential is a diffusion potential with K+ and Cl− the most permeable ions. After depolarizing the basolateral membrane with high serosal potassium bathing solutions and eliminating the apical membrane as a rate limiting step for ion movement using the polyene antibiotic nystatin, we found that the addition of equal aliquots of NaCl to both solutions caused the basolateral membrane potential to hyperpolarize by up to 20 mV (cell interior negative). This popential was reduced by 80% within 3 min of the addition of ouabain to the serosal solution. This hyperpolarization most probably represents a ouabain sensitive active transport process sensitive to intracellular Na+. An equivalent electrical circuit for Na+ transport across rabbit urinary bladder is derived, tested, and compared to previous results. This circuit is also used to predict the effects that microelectrode impalement damage will have on individual membrane potentials as well as time-dependent phenomena; e.g., effect of amiloride on apical and basolateral membrane potentials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01972629
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  • 3
    Electronic Resource
    Electronic Resource
    Active and passive properties of rabbit descending colon: A microelectrode and nystatin study (1979)
    Springer
    The journal of membrane biology 45 (1979), S. 81-108 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The electrical properties of the basolateral membrane of rabbit descending colon were studied with microelectrode methods in conjunction with the polyene antibiotic nystatin. Two problems were examined: (i) the relative distribution of tight junctional, apical membrane and basolateral membrane resistances, and (ii) the ionic basis of the basolateral membrane potential. Intracellular K+ activity (K+) was measured using liquid ion exchanger microelectrodes ((K+)=76±2mm) and was found not to be in equilibrium with the basolateral membrane potential. In order to measure membrane resistances and to estimate the selective permeability of the basolateral membrane, the apical membrane was treated with nystatin and bathed with a K2SO4 Ringer's solution which was designed to mimic intracellular K+ composition. This procedure virtually eliminated the resistance and electromotive force of the apical membrane. Shunt resistance was calculated by two independent methods based on microelectrode and transepithelial measurements. Both methods produced similar results (R s =691±63 Ω cm2 and 770±247 Ω cm2, respectively). These findings indicate that the shunt has no significant selectivity, contrary to previous reports. Native apical membrane resistance was estimated as 705±123 V cm2 and basolateral membrane resistance was 95±14 V cm2. To estimate basolateral membrane selectivity, the serosa was bathed in a NaCl Ringer's solution followed by a series of changes in which all or part of the Na+ was replaced by equimolar amounts of K+. From measures of bi-ionic potentials and conductance during these replacements, we calculated potassium permeability and selectivity ratios for the nystatin-treated colon by fitting these results to the constant field equations. By correcting for shunt conductance, it was then possible to estimate the selective permeability of the basolateral membrane alone. Selectivity estimates were as follows:P Na/P K=.08 andP Cl/P K=.07 (uncorrected for shunt) andP Na/P K=.04 andP Cl/P K=.06 (basolateral membrane alone). In a second set of experiments, evidence for an electrogenic Na+ pump in the basolateral membrane is presented. A small ouabain-sensitive potential could be generated in the nystatin-treated colon in the absence of chemical or electrical gradients by mucosal, but not serosal, addition of NaCl. We conclude that this electrogenic pump may contribute to the basolateral membrane potential; however, the primary source of this potential is “passive”: specifically, a potassium gradient which is maintained by an “active” transport process. An appendix compares the results of nystatin experiments to amiloride experiments which were conducted separately on the same tissues. The purpose of this comparison was to develop a comprehensive model of colonic transport. The analysis reveals a leak conductance in the apical membrane and the presence of an amiloride-insensitive conductance pathway.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869296
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  • 4
    Electronic Resource
    Electronic Resource
    Cation selectivity of the resting membrane of squid axon (1972)
    Springer
    The journal of membrane biology 9 (1972), S. 373-384 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Permeability constant ratios among monovalent cations were studied in the resting membrane of a giant axon of a Pacific squid,Loligo opalescens, by observing the relationship between the membrane potential and the ion concentration. The average permeability ratios are: Tl, 1.8; K, 1.0; Rb, 0.72; Cs, 0.16; Na, 〈0.08; Li, 〈0.08. These permeability ratios suggest that neither valinomycin nor nonactin are adequate models for the sites producing the resting permeability in the axonal membrane. Cyclic polyetherbis(t-butyl cyclohexyl) 18-crown-6 does not increase the permeability ratioP Cs/P K except when applied at concentrations (5×10−5 m) at which the surfactant properties of this molecule may become significant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868063
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  • 5
    Electronic Resource
    Electronic Resource
    Ionic permeabilities of anAplysia giant neuron (1975)
    Springer
    The journal of membrane biology 21 (1975), S. 353-374 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary In a giant neuron ofAplysia californica, permeabilities and conductances obtained by measuring net fluxes of Na+, K+ and Cl− with ion-specific microelectrodes were compared with those obtained by measuring transmembrane current and potential changes when the three ions were varied in the external solution. Net fluxes were measured with ion-specific microelectrodes, after blocking metabolic processes, thus allowing movement of ions down their electrochemical gradients. Permeabilities and conductances obtained from the “chemical” measurements (i.e., ion-specific electrodes) were generally comparable to the values obtained from “electrical” measurements. Where discrepancies occurred, they could be explained by showing that some of the assumptions necessary to use the “electrical” method were not quantitatively true in this system. The absolute magnitudes of the permeabilities are significantly less than those found in many axonal preparations. There is also a relatively highP Na/P K ratio. The selectivity of the membraneagainst ions such as Tris+ and MeSO 3 − is not good, Tris+ being nearly as permeable as Na+ and MeSO 3 − about one-half as permeable as Cl−. These properties may be characteristic of somal membranes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01941076
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  • 6
    Electronic Resource
    Electronic Resource
    Fed-batch and continuous fermentation ofSelenomonas ruminantium for natural propionic, acetic and succinic acids (1995)
    Springer
    Journal of industrial microbiology and biotechnology 15 (1995), S. 32-38 
    Details
    ISSN: 1476-5535
    Keywords: corn steep liquor ; yeast extract ; lactic acid ; sodium sulfide ; cysteine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract An anaerobic fermentation process was developed for production of natural propionic, acetic and succinic acids froml-lactic acid usingSelenomonas ruminantium. Thel-lactic acid was quickly converted to a racemic mixture and there was no enantiomeric preference for further metabolism. The lactic acid was metabolized to propionic, acetic and succinic acids typically in a molar ratio of about 5∶3∶1. However, the ratio of propionate: succinate started high (as much as 22∶1), before declining to as low as 5∶1 after the first 48 h. Nutrients in corn steep liquor and yeast extract were necessary for optimal production of propionic acid. The corn steep liquor and yeast extract were heat stable at neutral pH, but some nutritional qualities were lost when heated at pH 2.4. In fed-batch fermentation on lactic acid 2.0% propionic acid was produced in 48 h and 2.3% in 68 h. A continuous culture operated at a dilution rate of 0.055 h−1 and a lactic acid feed concentration of 30 gL−1 had a propionic acid productivity of 0.59 gL−1h−1. The steady state results were: lactic acid 0.6%, propionic acid 1.1%, acetic acid 0.50%, and succinic acid 0.33%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01570010
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