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  • 1
    Electronic Resource
    Electronic Resource
    The interpretation of intracellular measurements of membrane potential, resistance, and coupling in cells of higher plants (1978)
    Springer
    Planta 143 (1978), S. 267-274 
    Details
    ISSN: 1432-2048
    Keywords: Cells (electric properties) ; Coleoptiles ; Electrical parameters ; Intercellular coupling ; Intracellular recording ; Membrane resistance ; Microelectrodes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Results of microelectrode impalements of parenchymal cells of coleoptiles made in several different laboratories differ widely. The highest membrane potentials correlate with lower input resistance and the presence of intercellular coupling, whereas high input resistance seems to be associated with an absence of measurable coupling and possibly lower membrane potentials. In this paper we demonstrate that these results are consistent with (1) a tonoplast resistance several times greater than the input resistance of the cytoplasmic compartment, and (2) the presence of variable amounts of shunting introduced by insertion of the microelectrode through the cell membranes. The general consequences of this hypothesis are developed quantitatively. If the ideas are applicable to other tissues of higher plants-and on this point the evidence is still insufficient to judgeboth the design of experiments and the interpretation of measurements made with microelectrodes will have to be reevaluated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00391997
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  • 2
    Electronic Resource
    Electronic Resource
    Dark adaptation, sensitivity, and rhodopsin level in the eye of the lobster,Homarus (1977)
    Springer
    Journal of comparative physiology 120 (1977), S. 143-159 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Dark adaptation of living lobsters was measured by recording the ERG at several temperatures in the range 5–20 °C following adapting flashes that convert about 70% of the rhodopsin to metarhodopsin. Recovery of log threshold is rapid, and at 10–20° is nearly complete in 10 min. Only at 5 °C is dark adaptation significantly slowed. Comparison of dark adaptation with data on regeneration of pigment (Bruno et al., 1977) is consistent with the hypothesis that as rhodopsin concentration rises and falls, its only effect on sensitivity is to alter the probability of quantum catch. This interpretation is further bolstered by observations on winter lobsters that have a 70% deficiency of rhodopsin without the concomitant increase in metarhodopsin that accompanies light adaptation. No effect of metarhodopsin on sensitivity was detected. These experiments support the growing body of evidence indicating that the relationship between rhodopsin concentration and log threshold is fundamentally different in the rhabdomeric photoreceptors of invertebrates and the rods and cones of vertebrates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00619311
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  • 3
    Electronic Resource
    Electronic Resource
    Discrimination of colors by the black-chinned hummingbird,Archilochus alexandri (1979)
    Springer
    Journal of comparative physiology 130 (1979), S. 209-220 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The color vision of a population of black-chinned hummingbirds was studied by behavioral methods. Birds were attracted to feeders equipped with tungsten lamps and interference filters. Results are based on counts of approximately 5700 visits by 92 ± 5 birds. Population size was estimated by mistnetting and marking 29 hummingbirds, 22 of which could be recognized individually during the course of the experiments. Following experience with red (620 nm) at all feeders, the birds showed a modest tendency to visit red (620 nm, 650 nm) and blue (490 nm) rather than intermediate greens and yellows. When sugar was presented at only one wavelength, however, choices became much sharper. When positions of the feeders were randomized, trained birds selected feeders on the basis of hue. Brightness was not used as a significant cue. This finding thus provides a more rigorous demonstration of color vision in hummingbirds than has heretofore been available. Either position or color could be learned in several hours (6–22 visits). Red (620 nm) and green (546 nm) were learned at the same rate. Two different (and opposing) color associations could be learned simultaneously at sites approximately 30 m apart. Discrimination of hue was measured following training to each of four wavelengths: 620, 590, 546, and 480 nm. Light from interference filters with transmission maxima at 546 and 550 nm were differentiated by the birds to a statistically significant extent. 546 and 590 nm appear to lie near the boundaries of hues; a boundary near 540 nm is found in pigeon but not human color vision.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00614607
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  • 4
    Electronic Resource
    Electronic Resource
    Responses of crayfish photoreceptor cells following intense light adaptation (1986)
    Springer
    Journal of comparative physiology 158 (1986), S. 35-42 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary After intense orange adapting exposures that convert 80% of the rhodopsin in the eye to metarhodopsin, rhabdoms become covered with accessory pigment and appear to lose some microvillar order. Only after a delay of hours or even days is the metarhodopsin replaced by rhodopsin (Cronin and Goldsmith 1984). After 24 h of dark adaptation, when there has been little recovery of visual pigment, the photoreceptor cells have normal resting potentials and input resistances, and the reversal potential of the light response is 10–15 mV (inside positive), unchanged from controls. The log V vs log I curve is shifted about 0.6 log units to the right on the energy axis, quantitatively consistent with the decrease in the probability of quantum catch expected from the lowered concentration of rhodopsin in the rhabdoms. Furthermore, at 24 h the photoreceptors exhibit a broader spectral sensitivity than controls, which is also expected from accumulations of metarhodopsin in the rhabdoms. In three other respects, however, the transduction process appears to be light adapted: (i) The voltage responses are more phasic than those of control photoreceptors. (ii) The relatively larger effect (compared to controls) of low extracellular Ca++ (1 mmol/1 EGTA) in potentiating the photoresponses suggests that the photoreceptors may have elevated levels of free cytoplasmic Ca++. (iii) The saturating depolarization is only about 30% as large as the maximal receptor potentials of contralateral, dark controls, and by that measure the log V-log I curve is shifted downward by 0.54 log units. The gain (change in conductance per absorbed photon) therefore appears to have been diminished.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00614518
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  • 5
    Electronic Resource
    Electronic Resource
    The visual pigment and visual cycle of the lobster,Homarus (1977)
    Springer
    Journal of comparative physiology 120 (1977), S. 123-142 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The visual pigment of the American lobster,Homarus americanus, has been studied in individual isolated rhabdoms by microspectrophotometry. Lobster rhodopsin has λmax at 515 nm and is converted by light to a stable metarhodopsin with λmax at 490 nm. These figures are in good agreement with corresponding values obtained by Wald and Hubbard (1957) in digitonin extracts. Photoregeneration of rhodopsin to metarhodopsin is also observed. The absorbance spectrum of lobster metarhodopsin is invariant with pH in the range 5.4–9, indicating that even after isomerization of the chromophore fromcis totrans, the binding site of the chromophore remains sequestered from the solvent environment. Total axial density of the lobster rhabdom to unpolarized light is about 0.7. As described for several other Crustacea, aldehyde fixation renders the metarhodopsin susceptible to photobleaching, a process that is faster at alkaline than at neutral or acid pH. Small amounts of a photoproduct with λmax at 370 nm are occasionally seen. A slower dark bleaching of lobster rhabdoms (τ1/2−2 h) also occurs, frequently through intermediates with absorption similar to metarhodopsin. The molar extinction coefficient of metarhodopsin is about 1.2 times greater than that of rhodopsin, each measured at their respective λmax. Isomerization of the chromophore fromcis totrans is accompanied by a change in the orientation of the absorption vector of about 3°. The absorption vector of metarhodopsin is either tilted more steeply into the membrane or is less tightly oriented with respect to the microvillar axes. When living lobsters are kept at room temperature, light adaptation does not result in an accumulation of metarhodopsin. At 4 °C, however, the same adapting lights cause a reduction of rhodopsin and an increase in metarhodopsin. There is thus a temperature-sensitive regeneration mechanism that supplements photoregeneration. Following 1 ms, 0.1 joule xenon flashes that convert about 70% of the rhodopsin to metarhodopsin in vivo, dark regeneration occurs in the living eye with half-times of about 25 and 55 min at 22 °C and 15 °C respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00619310
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  • 6
    Electronic Resource
    Electronic Resource
    Photosensitivity of retinular cells in white-eyed crayfish (Procambarus clarkii) (1977)
    Springer
    Journal of comparative physiology 122 (1977), S. 273-288 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. The eyes of a white-eyed mutant of the crayfishProcambarus clarkii have been examined by several techniques. The white phenotype is due to the absence of the distal and retinular screening pigments. The accessory pigments, around the basal ends of the rhabdoms, are still present. As in the wild-type, the accessory pigments are white in reflected light and brown in transmitted light. 2. Animals kept in darkness for several days have normal rhabdoms. Difference spectra for total bleaches have λmax at 531 nm, and the metarhodopsin has λmax at 515 nm. These pigments are spectrally indistinguishable from the rhodopsin and metarhodopsin of wild-type crayfish. 3. Several days exposure to normal indoor lighting causes extensive atrophy of the rhabdom and loss of visual pigment, as well as a 70-fold decrease in sensitivity. 4. Spectral sensitivity of the eye (ERG) has λmax at about 560 nm (close to the wild-type) after several days in darkness, but shifts to 546 nm as the rhabdoms atrophy. Neither curve is displaced by adaptation with blue light. Both values are red-shifted from the λmax of the pigment of the rhabdom, most likely by the accessory screening pigment. The shift is smaller when the screening pigment is separated from the (atrophied) rhabdom by several μm. 5. If the distal screening pigments of the wild-type are removed surgically and precautions are taken to stabilize the effects of remaining screening pigments, intracellular recordings have λmax at 562 nm and show much less variation than has previously been reported. 6. The mutant, like the wild-type, has violet receptors whose contribution to the ERG is unmasked by long wavelength adaptation. Their λmax is at 440 nm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00611895
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  • 7
    Electronic Resource
    Electronic Resource
    Four spectral classes of cone in the retinas of birds (1986)
    Springer
    Journal of comparative physiology 159 (1986), S. 473-479 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The spectral sensitivity of 15 species of birds has been measured by recording transretinal voltages from opened eyecups. With suitable combinations of colored adapting lights, we find that a variety of passerines have four peaks of photopic sensitivity, with maxima at 370, 450, 480, and 570 nm. Additional sensitivity maxima at 510 nm are found in some species. The spectral sensitivity functions are not altered by bathing the retinas in 50 mM sodium aspartate, suggesting that they reflect the properties of cones and do not result from inhibitory interactions between retinal interneurons. Comparison of the results with a general mathematical model that describes spectral sensitivity functions recorded extracellularly from populations of receptors in different states of adaptation (Goldsmith 1986) shows that the retinal spectral sensitivity functions are consistent with the presence of (at least) four types of cone, but indicate as well that many of the cones that are maximally sensitive in the blue and violet likely contain oil droplets that attenuate the deep violet and near uv.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00604167
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  • 8
    Electronic Resource
    Electronic Resource
    Interpreting trans-retinal recordings of spectral sensitivity (1986)
    Springer
    Journal of comparative physiology 159 (1986), S. 481-487 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary A quantitative model is developed to describe spectral sensitivity functions recorded extracellularly from heterogeneous populations of receptors in different states of adaptation. This treatment identifies the most important influences and clarifies several general features of experimental results. 1. The shapes of retinal spectral sensitivity curves in different states of chromatic adaptation depend in predictable fashion on whether the primary effect of the adapting light on individual receptors is to decreaseV max (response compression) or to increase the quantum demand for half-saturation. Some response compression is necessary in order for one or more receptors to drop out of the response at modest levels of adaptation. The apparent ease of adaptation also depends on the criterion voltage, particularly in the presence of response compression. 2. The technique of selective adaptation of the ERG is capable of revealing the presence of receptors that comprise only a few percent of the total population. 3. The short wavelength absorption of all visual pigments normally makes it impossible to use uv or violet light to adapt selectively those receptors with maximal sensitivity in the uv or violet region of the spectrum while sparing receptors with maximal sensitivity at longer wavelengths. The presence of cone oil droplets absorbing at short wavelengths, however, can effectively screen visual pigments in some of the receptors from uv or violet adapting lights.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00604168
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  • 9
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    The interpretation of intracellular measurements of membrane potential, resistance, and coupling in cells of higher plants (1978)
    Springer
    Details
    Publication Date: 1978-01-01
    Print ISSN: 0032-0935
    Electronic ISSN: 1432-2048
    Topics: Biology
    Published by Springer
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  • 10
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    Early Events in Vision: Vertebrate Photoreception . Papers from a symposium, London, Sept. 1976. H. B. Barlow and P. Fatt, Eds. Academic Press, New York, 1977. xx, 380 pp., illus. $29. (1979)
    American Association for the Advancement of Science
    Details
    Publication Date: 1979-02-16
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science
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