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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    European biophysics journal 20 (1991), S. 65-69 
    ISSN: 1432-1017
    Schlagwort(e): Airway epithelium ; Asthma ; Apical membrane ; Ion channel kinetics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Physik
    Notizen: Abstract The single channel inside-out patch clamp technique was used to characterize ion channels in the apical membranes of ragweed-sensitized and control canine tracheal epithelial cells maintained in primary culture. Patches were obtained from single isolated cells or from cells at the edges of confluent sheets. A new type of chloride channel was seen in sensitized cells but not in control cells. The channel showed inward rectification in symmetric chloride solutions with conductance varying from 95 pS to 52 pS over the range of −60 mV to 60 mV membrane potential. Channel gating was voltage dependent with maximal opening at about −30 mV Kinetic analysis showed that distributions of closed and open times could both be well fitted by the sums of three exponential components. Rate constants for transitions between the states of a linear kinetic model were calculated, with only one rate being significantly voltage dependent. The possible significance of this channel is discussed.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Annals of biomedical engineering 26 (1998), S. 308-314 
    ISSN: 1573-9686
    Schlagwort(e): Visual acuity ; Motion detection ; Impulse response ; Adapting bump model ; Photoreceptors
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Abstract The responses of photoreceptor cells to moving stimuli are crucial to understanding motion detection in visual systems. However, these responses are not well characterized quantitatively because they result from a combination of spatial optical behavior in the lens systems with temporal behavior in the phototransduction mechanism. While both these processes can now be modeled quite well by relatively simple equations, their combination cannot be easily obtained in a closed form. Here, we present two approaches to this problem, based on well-established models for the lens and photoreceptors systems of the fly compound eye. The first approach leads to a recursive formula for predicting the photoreceptor response to a moving point object. The second method is approximate, but almost equally accurate and more rapid. © 1998 Biomedical Engineering Society. PAC98: 4266Lc, 8722-q, 8710+e
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Annals of biomedical engineering 23 (1995), S. 70-77 
    ISSN: 1573-9686
    Schlagwort(e): Phototransduction ; Light adaptation ; Gamma function ; Impulse response
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Abstract Light-adapted fly photoreceptor cells were stimulated with brief positive and negative contrast flashes (contrast=ΔI/I, I=intensity). Membrane potential responses to a wide range of flash intensities were well-fitted by a static nonlinearity followed by a compartmental model represented by a gamma function. However, the agreement improved if one parameter of the gamma function,n, varied quadratically with input light intensity. Response amplitude and time to peak were estimated from the fitted parameters. Response amplitude varied approximately linearly with contrast but showed nonlinear compression with the largest negative flashes. Reducing the background light level by 3 decades or hyperpolarizing the cell electrically produced stronger nonlinear compression with both contrast polarities. This is probably due to fast voltage-activated K+ channels. Responses to double flashes with varying time separations were well-fitted by summed gamma functions, allowing separation of the individual flash responses. There was no detectable time-dependent interaction between paired positive flashes at all separations. However, the response to two negative flashes was greater than the linear prediction at short separations, and this facilitatory nonlinearity decayed with a time constant of about 1 msec. The facilitation is probably related to resonant behavior in light-adapted photoreceptors and may be due to an IP3-induced intracellular Ca2+ release.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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