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K Kirschfeld

Publications and source records attributed to K Kirschfeld.

At least 37 records · Page 2Linked to original sources
PubMed1993

Spectral tuning of rhodopsin and metarhodopsin in vivo.

Color vision is dependent upon the expression of spectrally distinct forms of rhodopsin in different photoreceptor cells. To identify the structural features of rhodopsin that regulate spectral sensitivity and absorption in vivo, we have constructed a series of chimeric Drosophila rhodopsin molecules, derived from a blue- and a violet-sensitive rhodopsin, and used P element-mediated germline transformation to generate transgenic flies that express the modified pigments in the R1-R6 photoreceptor cells of the compound eye. Our analysis of these animals indicates that multiple regions of the opsin protein are involved in regulating rhodopsin spectral sensitivity and that the native and photoactivated forms of rhodopsin can be tuned independently of each other. These results demonstrate the feasibility of designing receptor molecules with specifically modified activated states.

Amino Acid Sequence↗
PubMed1993

Optics of the harbor porpoise eye in water.

A two-dimensional ray-tracing model for the harbor porpoise eye is constructed from new measurements, mainly on two enucleated eyes, and from data found in the literature. Model calculations show that the crystalline lens has too much refractive power to focus light on the retina. The cornea has a high refractive index and acts as a diverging lens of considerable refractive power. The cornea corrects the eye to near emmetropia for axial and temporal (caudal) directions of view. The eye is approximately 5-D myopic for nasal (frontal) directions of view. The iris serves a dual role as a stop: the iris determines the shapes of bundles of light that enter the lens and the iris blocks light that leaves the lens anterior to its equator.

Animals↗
PubMed1992

Enflurane is a potent inhibitor of high conductance Ca(2+)-activated K+ channels of Chara australis.

The volatile anaesthetic, enflurane, is commonly used in surgery for inducing the state of general anaesthesia. It is assumed, that general anaesthetics act on ion channels, but little is known of how they do so and what kinds of channels are sensitive. We found, that enflurane inhibits a large conductance Ca(2+)-activated K+ channel of the green alga, Chara australis. Effects occur at clinically relevant concentrations are fully reversible. The actions of enflurane are distinct from those of charybdotoxin and tetraethylammonium, which are well known blockers of this channel type. Kinetic analysis of single-channel data demonstrates multiple effects of enflurane on the channel protein.

Calcium↗
PubMed1992

Oscillations in the insect brain: do they correspond to the cortical gamma-waves of vertebrates?

gamma-waves, relatively high-frequency oscillations (30-80 Hz) that can be recorded in the olfactory system and the visual cortex of vertebrates, have recently attracted much attention. A role as an information carrier is under discussion, a possible involvement in "feature linking" has been suggested, and they have also been implicated functionally in phenomena such as mind consciousness or awareness. It has long been known that stimulus-dependent high-frequency oscillations (hf waves) can also be recorded from the optic lobes of arthropods. These oscillations in flies have been examined and found to be analogous to the gamma-waves in many respects. Based on knowledge of the anatomy and physiology of the visual system in flies, the most plausible interpretation of the function of these oscillations differs from the interpretations of the vertebrate gamma-waves currently under consideration.

Animals↗
PubMed1992

The nss mutation or lanthanum inhibits light-induced Ca2+ influx into fly photoreceptors.

Ion-selective calcium microelectrodes were inserted into the compound eyes of the wild-type sheep blowfly Lucilia or into the retina of the no steady state (nss) mutant of Lucilia. These electrodes monitored light-induced changes in the extracellular concentration of calcium (delta[Ca2+]o) together with the extracellularly recorded receptor potential. Prolonged dim lights induced a steady reduction in [Ca2+]o during light in the retina of normal Lucilia, while relatively little change in [Ca2+]o was observed in the retina of the nss mutant. Prolonged intense light induced a multiphasic change in [Ca2+]o: the [Ca2+]o signal became transient, reaching a minimum within 6 s after light onset, and then rose to a nearly steady-state phase below the dark concentration. When lights were turned off, a rapid increase in [Ca2+]o was observed, reaching a peak above the dark level and then declining again to the dark level within 1 min. In analogy to similar studies conduced in the honeybee drone, we suggest that the reduction in [Ca2+]o reflects light-induced Ca2+ influx into the photoreceptors, while the subsequent increase in [Ca2+]o reflects the activation of the Na-Ca exchange which extrudes Ca2+ from the cells. In the nss mutant in response to intense prolonged light, the receptor potential declines to baseline during light while the Ca2+ signal is almost abolished, revealing only a short transient reduction in [Ca2+]o. Application of lanthanum (La3+), but not nickel (Ni2+), into the retinal extracellular space of normal Lucilia mimicked the effect of the nss mutation on the receptor potential, while complete elimination of the Ca2+ signal in a reversible manner was observed. The results suggest that La3+ and the nss mutation inhibit light-induced Ca2+ influex into the photoreceptor in a manner similar to the action of the trp mutation in Drosophila, which has been shown to block specifically a light-activated Ca2+ channel necessary to maintain light excitation.

Animals↗
PubMed1992

Ectopic expression of ultraviolet-rhodopsins in the blue photoreceptor cells of Drosophila: visual physiology and photochemistry of transgenic animals.

We have generated transgenic flies expressing R7 cell-specific opsins in the major class of photoreceptor cells of the Drosophila retina and characterized their spectral properties using high-resolution microspectrophotometry and sensitivity recordings. We show that the Rh3 and Rh4 opsin genes encode UV-sensitive opsins with similar spectral properties (lambda max = 345 nm and 375 nm), and that Rh3 corresponds to the R7p and R7marg class of visual pigments. We have also generated Rh3 and Rh4 isoform-specific antibodies and present an R7 cell map of the Drosophila retina. In a related set of experiments, we show that it is possible to coexpress two different visual pigments functionally in the same cell and produce photoreceptors that display the summed spectral response of the individual pigments. These findings open up the possibility of tuning an animal's visual behavior by targeted expression of combinations of opsin genes to selective types of photoreceptors.

Animals↗
PubMed1991

An optomotor control system with automatic compensation for contrast and texture.

When an animal's surroundings move, the animal normally follows that movement by turning its eyes (that is, by an optomotor reaction). As a result, the retinal image is partly stabilized. The efficacy of this stabilization necessarily depends on the gain of the optomotor control circuit. So far no biological detectors of retinal image movements have been discovered in either vertebrates or invertebrates that is, elements capable of generating a signal proportional to the movement velocity, which could serve as sensors in this control system (Borst & Egelhaaf 1989). The reason is that many other parameters, such as the light intensity and the 'texture' of the pattern, also affect the neuronal output. If movement detection is texture dependent, for instance, the gain and hence the quality of stabilization must also be texture dependent. But in humans, at least, with large-field stimulation the quality of retinal image stabilization has been found to be largely independent of texture (de Graaf et al. 1990). Here I describe a control system with gain control that permits automatic compensation, under closed-loop conditions, of the dependence of movement detection on parameters such as texture, brightness and so on. Comparison with data from experiments on arthropods shows that, in these animals at least, a control circuit with nonlinear properties like those suggested here has in fact been realized.

Animals↗
PubMed1990

The pigeon's eye viewed through an ophthalmoscopic microscope: orientation of retinal landmarks and significance of eye movements.

The retina of live, anaesthetized pigeons was inspected with an ophthalmoscopic microscope mounted on a goniometer. Retinal landmarks (optic axis, pecten, fovea, border between the yellow and red field) and the ora terminalis were projected into the visual field of the eye and related to existing data. The resting position of the eye is determined by an orientation of the pecten 45 degrees to the horizontal plane and the optic axis pointing to the horizon with an azimuth angle of 70 degrees relative to the bill. The binocular overlap is maximal (approximately 30 degrees) some 15 degrees above the eye-bill axis. In the resting position of the eye the red field is directed to the lower frontal visual field with only marginal binocular overlap. Binocular overlap of the area dorsalis with the red field, however, during frontal fixation is brought about by eye movements in the range we have demonstrated. The fixation point is 10 degrees below the eye-bill axis.

Animals↗
PubMed1988

The neuronal basis of the anesthetic state: a comparative physiological approach. II. The influence of anesthetics on various reactions in flies.

The sensitivity of specific neuronal pathways to Halothane and N2O has been investigated in flies. The effects were tested by monitoring the responses of photoreceptors and their second order neurons, as well as two behavioral responses--a leg reflex induced by light flashes and head movements induced by moving optical patterns--chosen because their neuronal substrates are fairly well known. Sensitivity to both agents rises with the length of dendrites and the number of input synapses of the neurons involved. The findings confirms the hypothesis, formulated in Part I of this paper, that neurons with long dendrites and/or axonal endings and large numbers of input synapses are the elements in the central nervous system with the highest sensitivity to anesthetic action. Under physiological conditions this kind of neuron is capable of "gain-control": the relationship between input and output is modified according to functional requirements. Possible molecular mechanisms leading to functional impairment under anesthesia are discussed.

Anesthesia↗
PubMed1986

Does retinol serve a sensitizing function in insect photoreceptors?

Spectral sensitivity of the dorsal compound eye of Simuliid males (Nematocera) shows a maximum in the u.v. at 340 nm, and a shoulder or second, smaller maximum around 430 nm. The visual pigment--based on retinal and therefore a rhodopsin--has its absorption maximum at 430 nm. The 340 maximum is due to a sensitizing pigment that transfers energy to the visual pigment. The properties of the Simuliid-photoreceptor hence are similar to most of the photoreceptors in higher flies (Musca, Calliphora, Drosophila), that also have a u.v.-absorbing sensitizing pigment. The difference is that in Simuliids the sensitizing pigment is not 3-hydroxyretinol as in the higher flies but a different substance, most likely retinol.

Animals↗
PubMed1985

The contribution of different colour receptors to a motor output in the fly.

A light flash given to the eye of Calliphora leads to a movement of the legs (light induced leg reflex) which most likely normally initiates flight of the animal. This reflex has a short latency (12 to 30 ms, depending upon light intensity) and is quite reproducible without habituation. The spectral sensitivity of the reflex shows that receptors R1-6 most likely govern the input to the reflex in dark adaptation, a contribution of receptors R7 can be demonstrated with selective chromatic adaptation.

Animals↗
PubMed1982

Carotenoid pigments: their possible role in protecting against photooxidation in eyes and photoreceptor cells.

The effect of light on animal tissues is ambivalent. Light is necessary for many functions, e.g. for vision and, as in the flagellate halobacterium, to gain energy. But light is potentially dangerous: it is capable of destroying cells or their components by photooxidation, especially in the presence of sensitizing pigments such as haems and cytochromes, which are ubiquitous in aerobic cells. Several different examples are discussed to show how a compromise is achieved in animal tissues that for functional reasons receive high exposure to light. Carotenoid pigments, present in many eyes and photoreceptors, seem especially suited to protect against the deleterious effects of light because they absorb the dangerous short wavelength part of the light spectrum. In plant tissue, carotenoids are also well known to be capable of 'quenching' photoexcited states of sensitizing pigments and of oxygen, a function that they might have also in animal tissue. A consequence of the considerations is that whenever animal tissues are exposed to higher than usual light levels and/or oxygen pressures cellular damage might occur. Examples are discussed; strategies to circumvent the deleterious effects by photooxidation follow directly from the arguments.

Adult↗
PubMed1981

Fluorescence of photoreceptor cells observed in vivo.

Most rhabdomeres in the eye of the fly (Musca domestica) are fluorescent. One kind of fluorescent emission emanates from a photoproduct of the visual pigment, other kinds may be ascribed to photostable pigments. These phenomena provide not only a means of spectrally mapping the retina but also a new spectroscopic tool for analyzing the primary visual processes in vivo.

Animals↗
PubMed1980

Reversible events in the transduction process of photoreceptors.

In photoreceptors, a latency of many milliseconds elapses between the absorption of a light quantum and the occurrence of the late receptor potential, even for strong light stimuli. Surprisingly, this is much longer than the time necessary for conductance changes such as occur in membranes of neurones or muscles, mediated by chemical transmitters. There are several possible explanations for the long photoreceptor latency. (1) It may be due to properties of the visual pigment molecules. For instance, the temporal coincidence of the occurrence of metarhodospin II with the receptor signal indicates that the meta I-meta II transition might be the trigger for the electrical response in vertebrate photoreception. (2) It may be explained by properties of transport processes. Such a time consuming process could be the diffusion of an internal 'transmitter substance', which diffuses to a 'pore' in the receptor membrane. (3) A third possibility is the time needed to produce and accumulate chemical substances. The light-induced change of the visual pigment molecule might trigger a chemical reaction chain, in which the product of an earlier step triggers the next one. The experiments described here show that a considerable part of the long latency in photoreception is due to processes that are localised at the level of the visual pigment molecule.

Animals↗
PubMed1980

Fast electrical potentials arising from activation of metarhodopsin in the fly.

The cellular origin and properties of fast electrical potentials arising from activation of Calliphora photopigment were investigated. It was found by intracellular recordings that only the corneal-negative M1 phase of fly M potential arises in the photoreceptors' membrane. This M1 phase has all the accepted characteristics of an early receptor potential (ERP). It has no detectable latency, it survives fixation with glutaraldehyde, it is linear with light intensity below pigment saturation, and it is linear with the amount of metarhodopsin activated by light. The Calliphora ERP was found, however, to be exceptional because activation of rhodopsin, which causes the formation of metarhodopsin in 125 microsecond (25 degrees C), was not manifested in the ERP. Also, the extracellularly recorded ERP was not proportional to the rate of photopigment conversion. The corneal-positive M2 phase of the M potential was found to arise from second-order lamina neurons (L neurons). Intracellular recordings from these cells showed a fast hyperpolarizing potential, which preceded the normal hyperpolarizing transient of these cells. This fast potential appeared only when metarhodopsin was activated by a strong flash. The data indicate that the intracellularly recorded positive ERP, which arises from activation of metarhodoposin, elicits a hyperpolarizing fast potential in the second-order neuron. This potential is most likely the source of the corneal-positive M potential.

Action Potentials↗
PubMed1979

The contribution of a sensitizing pigment to the photosensitivity spectra of fly rhodopsin and metarhodopsin.

Most of the photoreceptors of the fly compound eye have high sensitivity in the ultraviolet (UV) as well as in the visible spectral range. This UV sensitivity arises from a photostable pigment that acts as a sensitizer for rhodopsin. Because the sensitizing pigment cannot be bleached, the classical determination of the photosensitivity spectrum from measurements of the difference spectrum of the pigment cannot be applied. We therefore used a new method to determine the photosensitivity spectra of rhodopsin and metarhodopsin in the UV spectral range. The method is based on the fact that the invertebrate visual pigment is a bistable one, in which rhodopsin and metarhodopsin are photointerconvertible. The pigment changes were measured by a fast electrical potential, called the M potential, which arises from activation of metarhodopsin. We first established the use of the M potential as a reliable measure of the visual pigment changes in the fly. We then calculated the photosensitivity spectrum of rhodopsin and metarhodopsin by using two kinds of experimentally measured spectra: the relaxation and the photoequilibrium spectra. The relaxation spectrum represents the wavelength dependence of the rate of approach of the pigment molecules to photoequilibrium. This spectrum is the weighted sum of the photosensitivity spectra of rhodopsin and metarhodopsin. The photoequilibrium spectrum measures the fraction of metarhodopsin (or rhodopsin) in photoequilibrium which is reached in the steady state for application of various wavelengths of light. By using this method we found that, although the photosensitivity spectra of rhodopsin and metarhodopsin are very different in the visible, they show strict coincidence in the UV region. This observation indicates that the photostable pigment acts as a sensitizer for both rhodopsin as well as metarhodopsin.

Animals↗