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T H Goldsmith

Publications and source records attributed to T H Goldsmith.

At least 37 records · Page 2Linked to original sources
PubMed1986

Responses of crayfish photoreceptor cells following intense light adaptation.

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: The voltage responses are more phasic than those of control photoreceptors. The relatively larger effect (compared to controls) of low extracellular Ca++ (1 mmol/l EGTA) in potentiating the photoresponses suggests that the photoreceptors may have elevated levels of free cytoplasmic Ca++. 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1986

Separation and identification of geometric isomers of 3-hydroxyretinoids and occurrence in the eyes of insects.

The 9-cis, 11-cis, 13-cis and all-trans isomers of 3-hydroxyretinal oxime, and the 11-cis, 13-cis and all-trans isomers of 3-hydroxyretinol have been resolved by high pressure liquid chromatography (HPLC) and identified by their spectral properties. The antimony chloride reaction product of 3-hydroxyretinol is spectrally indistinguishable from that of retinol. Heads of insects from 8 genera of Diptera and Lepidoptera were found to contain 3-hydroxyretinoids. The most abundant isomers of 3-hydroxyretinal are 11-cis and all-trans.

Animals↗
PubMed1984

The ultraviolet receptor of bird retinas.

The eyes of 15 species of birds from 10 families have some cones maximally sensitive at 370 nanometers in the near-ultraviolet. Spectral sensitivity was measured by recording extracellularly in opened eyecups , and a maximum in the ultraviolet was revealed by selectively adapting the retina with yellow background lights. The 370-nanometer spectral sensitivity function is attributed to receptors because its spectral position does not vary with the strength of adaptation and because it is present when the receptor potentials are isolated from the contributions of higher order retinal neurons by exposing the retina to sodium aspartate. These measurements demonstrate the basis for the ultraviolet sensitivity of birds that has been seen in behavioral experiments, and they provide further evidence that many vertebrates share with insects vision in the near-ultraviolet.

Animals↗
PubMed1984

Appearance of a Purkinje shift in the developing retina of the chick.

The development of rod and cone function was studied in late embryonic and posthatch chicks by measuring the spectral sensitivity of the electroretinogram (ERG) of opened eyecups to 100-msec flashes and 25-Hz stimuli. At the time of hatching the ERG is dominated by cone activity: the response-energy curves for different wavelengths are parallel, and the spectral sensitivity of the dark-adapted eye is maximal near 580 nm. During the first week after hatching, rods make a progressively greater contribution to the ERG: the response-energy functions cease to be parallel, and the spectral sensitivity maximum to dim flashes moves to about 510 nm while the maximum for brighter lights remains at 580 nm. Only the cones are able to follow the 25-Hz stimulus. Spectral sensitivity of the eye to 25-Hz stimuli, measured on red- or orange-adapting backgrounds, reveals the presence at the time of hatching of two photopic processes with lambda max at 415 nm and 580 nm, with evidence for a third in the region 470-510 nm.

Animals↗
PubMed1984

The cone oil droplets of avian retinas.

The cone oil droplets of 19 species of birds from 11 families were examined by microspectrophotometry. Individual droplets were expanded with mineral oil, suspended in aqueous glycerol, and absorbance spectra measured between 700 and 320 nm. A classification of oil droplets is proposed, in which objective measurements of their carotenoids are related to the size, position and visual appearance of the droplets under the microscope. Some droplets contain no carotenoid and are transparent at wavelengths longer than 320 nm. Other droplets appear colorless but contain carotenoids absorbing at 385 or 402 nm. The pale droplets that have traditionally been described as greenish contain a mixture of two carotenoids. All of these types are distinct from yellow and red droplets. Red droplets contain astaxanthin esters, and yellow droplets contain a carotenoid with a spectrum similar to zeaxanthin. The 402 nm chromophore is galloxanthin, a C27 apo-carotenoid with 8 double bonds. The in vivo optical densities are 1-4 in the paler droplets, range up to about 8 in the yellow droplets, and can exceed 20 in the red droplets. All droplets that contain carotenoid can exhibit substantial absorption in the near u.v. The frequencies of the several droplet types in the retinas of different species suggests that these organelles respond readily to natural selection and may be involved in more than one function.

Animals↗
PubMed1984

Dark regeneration of rhodopsin in crayfish photoreceptors.

The eyes of crayfish were exposed to lights of known spectral composition, and the course of regeneration was followed in the dark by measuring the content of rhodopsin and metarhodopsin in single rhabdoms isolated at various times after the adaptation, using an assay that is based on the fluorescence of metarhodopsin. Complete recovery requires several days in the dark after intense adaptation to orange light, but requires less than 2 d after blue light exposure. Following an orange light exposure with blue produces recovery kinetics characteristic of the blue light exposure alone. This quickening of recovery occurs whether the receptors are exposed to blue light either immediately or many hours after the original exposure to orange. Conversely, following blue light adaptation with orange leads to slow recovery, which is characteristic of orange alone. Recovery from long-wavelength adaptation is slower principally because many rhabdoms seem to delay the onset of regeneration. We suggest that the regeneration system is itself photosensitive, and after orange light adaptation the supply of active chromophore (presumably 11-cis retinal) limits the rate of recovery. Once started, recovery proceeds slowly and continuously, and the total pigment concentration (rhodopsin plus metarhodopsin) in the rhabdomeric membrane remains approximately constant. Within hours after intense adapting exposures, the rhabdoms become altered in appearance, the surfaces become coated with accessory pigment, and the bands of microvilli are less distinct. These changes persist until recovery of rhodopsin proceeds, which suggests that visual pigment regeneration results from addition of newly synthesized rhodopsin associated with membrane turn-over.

Animals↗
PubMed1982

Spectral dimorphism of crayfish visual pigment in solution.

Crayfish (Procambarus) photoreceptor membranes were prepared by a new technique. Digitonin extracts made at 0 degrees contain two rhodopsin-like pigments, P562 and P512, in a ratio of about 5:4. On exposure to light at 10 degrees C, P562 is converted to a metarhodopsin-like photoproduct with lambda max at 515 nm (M515), and P512 is converted to a metarhodopsin-like photoproduct with lambda max at 475 nm (M475). When warmed to 22 degrees C, both photoproducts bleach in minutes to retinal and opsin. Neither P562 nor P512 is attacked by hydroxylamine, but both are destroyed by the detergent Ammonyx LO and by reduction of disulfide bridges with 2-mercaptoethanol. Neither is altered by changing the concentration of Cl-. P562 is more susceptible than P512 to thermal denaturation and attack by OH-, and its spectrum is distinctly narrower than predicted by an Ebrey-Honig nomogram. P562 and P512 do not interconvert, either in the dark or in the presence of light. P512 is distinct from M515; it is substantially more stable at 22 degrees C and has a 23% smaller molar extinction coefficient. On the other hand, M515 is spectrally very similar to the single metarhodopsin that is formed by irradiation of rhabdoms from dark-adapted crayfish. As neither P562 nor P512 is found by irradiation of rhabdoms from dark-adapted crayfish. As neither P562 nor P512 is found in crayfish rhabdoms, we conclude that both pigments are created in digitonin micelles from a spectrally and kinetically homogeneous population of rhodopsin molecules with lambda max near 530 nm in the rhabdom.

Adaptation, Ocular↗
PubMed1982

Photosensitivity spectrum of crayfish rhodopsin measured using fluorescence of metarhodopsin.

Discrepancies exist among spectral measurements of sensitivity of crayfish photoreceptors, their absorption in situ, and the number and absorption spectra of crayfish photopigments that are extracted by digitonin solutions. We have determined the photosensitivity spectrum of crayfish rhodopsin in isolated rhabdoms using long wavelength fluorescence emission from crayfish metarhodopsin as an intrinsic probe. There is no measurable metarhodopsin in the dark-adapted receptor, so changes in the emission level are directly proportional to metarhodopsin concentration. We therefore used changes in metarhodopsin fluorescence to construct relaxation and saturation ("photoequilibrium") spectra, from which the photosensitivity spectrum of crayfish rhodopsin was calculated. This spectrum peaks at or approximately 530 nm and closely resembles the previously measured difference spectrum for total bleaches of dark-adapted rhabdoms. Measurements of the kinetics of changes in rhabdom fluorescence and in transmittance at 580 nm were compared with predictions derived from several model systems containing one or two photopigments. The comparison shows that only a single rhodopsin and its metarhodopsin are present in the main rhabdom of crayfish, and that other explanations must be sought for the multiple pigments seen in digitonin solution. The same analysis shows that there is no detectable formation of isorhodopsin in the rhabdom.

Adaptation, Physiological↗
PubMed1981

Fluorescence of crayfish metarhodopsin studied in single rhabdoms.

Isolated photoreceptor organelles (rhabdoms) from eyes of crayfish (Procambarus. Orconectes) were examined on a microscope system designed for quantitative measurements of fluorescent. Although fully dark-adapted rhabdoms are nonfluorescent or very weakly fluorescent, an increasing emission appears on exposure to light. Over the 30-fold range of intensities studied, the rate of the appearance of this fluorescence is identical to the rate of formation of metarhodopsin from rhodopsin. Furthermore, the excitation spectra for the observed emission are similar to the absorption spectra of crayfish metarhodopsin at both neutral and acid pH. Finally, the amount of fluorescence observed in rhabdoms previously irradiated with selected wavelengths of light is proportional to the amount of metarhodopsin present in the photosteady state established by the prior irradiation. The emission therefore originates from crayfish metarhodopsin. Fluorescence emission peaks at 670 nm at neutral pH. The quantum efficiency is 1.6 +/- 0.4 X 10(-3). Although emission from other rhodopsin photoproducts has previously been noted, this is the first description of fluorescence from the metarhodopsin chromophore site.

Animals↗
PubMed1981

Mathematical analysis of the chemosmotic polar diffusion of auxin through plant tissues.

Equations have been developed to describe the diffusional movement of a weak acid such as the auxin indoleacetic acid through a long file of vacuolated cells, where cellular accumulation is driven by the pH gradients across the cell membranes. If the permeability to the auxin anion is greater at one end of the cell than at the other, diffusional movement takes the form of polar transport, which exhibits: a nearly constant velocity either for the front or for a pulse of radioactive auxin, the capacity to move auxin against an external gradient of concentration, and a polar ratio that increases exponentially with the length of the section. The determinants of velocity include both diffusion through the vacuole and permeation steps at the cell membranes. Except for the permeabilities of the membranes to the anion, values are now available for all of the physical parameters in the equations. With reasonable estimates of permeability coefficients for the anion, the equations predict a velocity of transport of about 1 cm hr(-1), which agrees well with measured values. The analysis indicates, however, that the underlying cellular polarity may be greater than has been heretofore assumed. We thus demonstrate that the hypothesis of chemosmotic polar diffusion is capable of accounting quantitatively for the major features of auxin transport and provides a theoretical framework whose elements can be tested in future experiments.

Journal Article↗
PubMed1981

Spectral properties of fluorescence induced by glutaraldehyde fixation.

Following fixation with glutaraldehyde, tissues or gelatin films fluoresce. This fluorescence can be enhanced more than thirtyfold by several minutes exposure to near ultraviolet light. Longer wavelengths produce a smaller effect. The enhanced fluorescence is maximally excited at 540 nm (half-band width about 45 nm), and fluorescence emission peaks at 560 nm. The rate of photoenhancement is independent of temperature in the 12--30 degrees C range. Photoenhancement is greater at alkaline than acid pH; the pH dependence involves a single acid binding group with pK = 7.3. These effects are not observed following treatment with paraformaldehyde or prior reduction with boranedimethylamine. Schiff base linkages between the bifunctional cross-linking reagent and free amino groups therefore seem to be involved. The effects of pH and wavelength on the photoenhancement of fluorescence are best accounted for by a kinetic scheme that includes both photogeneration of fluorophore from an ultraviolet-absorbing precursor, and its subsequent photodestruction by visible light.

Aldehydes↗
PubMed1980

Hummingbirds see near ultraviolet light.

Three species of hummingbird (Archilochus alexandri, Lampornis clemenciae, and Eugenes fulgens) were trained to make visual discriminations between lights of different spectral content. On the basis of initial choices of feeders following a period of conditioning, birds of all three species were able to distinguish near ultraviolet (370 nanometers, 20-nanometer half bandwidth) from darkness (unilluminated viewing screen) or from the small amount of far red light that leaked through the ultraviolet-transmitting glass filter. A human observer was unable to make either discrimination. The birds were also able to distinguish white lights lacking wavelengths shorter than 400 nanometers from the full spectrum of the quartz-halogen bulbs. One can infer that the cone oil droplets, which have been lost from the retinas of most mammals, provide a potentially more flexible system for restricting the short wavelength end of the visible spectrum than does the filtering action of lens and macula that serves this function in the human eye.

Animals↗
PubMed1977

Restrictions on rotational and translational diffusion of pigment in the membranes of a rhabdomeric photoreceptor.

Individual, isolated rhabdoms from dark-adapted crayfish (Orconectes, Procambarus) were studied with a laterally incident microbeam that could be placed in single stacks of microvilli. Concentration gradients of metarhodopsin along the lengths of microvilli were produced by local bleaches, accomplished by irradiation with small spots of orange light at pH 9 in the presence of glutaraldehyde or formaldehyde. No subsequent redistribution of pigment was observed in the dark, indicating an absence of translational diffusion. On the basis of comparison with other systems, glutaraldehyde, but not formaldehyde (0.75%), would be expected to prevent diffusion of protein in the membrane. Under the same conditions photodichroism is observed, indicating an absence of free Brownian rotation. Photodichroism is larger in glutaraldehyde than in formaldehyde, suggesting that the bifunctional reagent quiets some molecular motion that is present after treatment with formaldehyde. Quantitative comparison of photodichroism with mathematical models indicates that the pigment absorption vectors are aligned within +/- 50 degrees of the microvillar axes and are tilted into the surface of the membrane at an average value of about 20 degrees. The photoconversion of rhodopsin to metarhodopsin is accompanied by an increase in molar extinction of about 20% at the lambda maxand a reorientation of the absorption vector by several degrees. The transition moment either tilts further into the membrane or loses some of its axial orientation, or both. The change in orientation is 3.5 time larger in formaldehyde than in glutaraldehyde.

Absorption↗