scholarly journals Light adaptation in retinal rods of the rabbit and two other nonprimate mammals.

1991 ◽  
Vol 97 (3) ◽  
pp. 413-435 ◽  
Author(s):  
K Nakatani ◽  
T Tamura ◽  
K W Yau
Keyword(s):  
Light Adaptation ◽  
Evoked Responses ◽  
Flash Intensity ◽  
Exponential Form ◽  
Time To Peak ◽  
Outward Currents ◽  
Retinal Rods ◽  
Response Peak ◽  
Flash Response ◽  
Plateau Level

The responses of rabbit rods to light were studied by drawing a single rod outer segment projecting from a small piece of retina into a glass pipette to record membrane current. The bath solution around the cells was maintained at near 40 degrees C. Light flashes evoked transient outward currents that saturated at up to approximately 20 pA. One absorbed photon produced a response of approximately 0.8 pA at peak. At the rising phase of the flash response, the relation between response amplitude and flash intensity (IF) had the exponential form 1-e-kappa FIF (where kappa F is a constant denoting sensitivity) expected from the absence of light adaptation. At the response peak, however, the amplitude-intensity relation fell slightly below the exponential form. At times after the response peak, the deviation was progressively more substantial. Light steps evoked responses that rose to a transient peak and rapidly relaxed to a lower plateau level. The response-intensity relation again indicated that light adaptation was insignificant at the early rising phase of the response, but became progressively more prominent at the transient peak and the steady plateau of the response. Incremental flashes superposed on a steady light of increasing intensity evoked responses that had a progressively shorter time-to-peak and faster relaxation, another sign of light adaptation. The flash sensitivity changed according to the Weber-Fechner relation (i.e., inversely) with background light intensity. We conclude that rabbit rods adapt to light in a manner similar to rods in cold-blooded vertebrates. Similar observations were made on cattle and rat rods.

scholarly journals Calcium regulates some, but not all, aspects of light adaptation in rod photoreceptors.

1989 ◽  
Vol 94 (2) ◽  
pp. 233-259 ◽  
Author(s):  
G D Nicol ◽  
M D Bownds
Keyword(s):  
Light Adaptation ◽  
Calcium Ionophore ◽  
Absolute Magnitude ◽  
Calcium Ionophore A23187 ◽  
Background Intensity ◽  
Ionophore A23187 ◽  
Background Illumination ◽  
Rod Photoreceptors ◽  
Time To Peak ◽  
Flash Response

The role of calcium as a regulator of light adaptation in rod photoreceptors was examined by manipulation of the intracellular Ca2+ concentration through the use of the calcium ionophore A23187 and external Ca2+ buffers. These studies utilized suspensions of isolated and purified frog rod outer segments that retain their mitochondria-rich inner segments (OS-IS). Three criteria of the dark- and light-adapted flash response were characterized as a function of the Ca2+ concentration: (a) the time to peak, (b) the rate of recovery, and (c) the response amplitude or sensitivity. For all Ca2+ concentrations examined, the time to peak of the flash response was accelerated in the presence of background illumination, suggesting that mechanisms controlling this aspect of adaptation are independent of the Ca2+ concentration. The recovery kinetics of the flash response appeared to depend on the Ca2+ concentration. In 1 mM Ca2+-Ringer's and 300 nM Ca2+-Ringer's + A23187, background illumination enhanced the recovery rate of the response; however, in 10 and 100 nM Ca2+-Ringer's + A23187, the recovery rates were the same for dark- and light-adapted responses. This result implies that a critical level of Ca2+ may be necessary for background illumination to accelerate the recovery of the flash response. The sensitivity of the flash response in darkness (SDF) was dependent on the Ca2+ concentration. In 1 mM Ca2+-Ringer's SDF was 0.481 pA per bleached rhodopsin (Rh*); a background of four Rh*/s decreased SDF by half (Io). At 300 nM Ca2+ + A23187, SDF was reduced to 0.0307 pA/Rh* and Io increased to 60 Rh*/s. At 100 nM Ca2+ + A23187, SDF was reduced further to 0.0025 pA/Rh* and Io increased to 220 Rh*/s. In 10 nM Ca2+ + A23187, SDF was lowered to 0.00045 pA/Rh* and Io raised to 760 RhI/s. Using these values of SDF and Io for each respective Ca2+ concentration, the dependence of the flash sensitivity on background intensity could be described by the Weber-Fechner relation. Under low Ca2+ conditions + A23187, bright background illumination could desensitize the flash response. These results are consistent with the idea that the concentration of Ca2+ may set the absolute magnitude of response sensitivity in darkness, and that there exist mechanisms capable of adapting the photoresponse in the absence of significant changes in cytoplasmic Ca2+ concentration.

Modulation of transduction gain in light adaptation of retinal rods

1994 ◽  
Vol 11 (1) ◽  
pp. 53-62 ◽  
Author(s):  
David R. Pepperberg ◽  
Jing Jin ◽  
Gregor J. Jones
Keyword(s):  
Visual Pigment ◽  
Light Adaptation ◽  
Peak Level ◽  
Background Intensity ◽  
Ambystoma Tigrinum ◽  
Flash Intensity ◽  
Rod Photoreceptors ◽  
Retinal Rods ◽  
Effect Of Light ◽  
Stimulation Of

AbstractThe effect of light adaptation on the period of photocurrent saturation induced by a bright stimulating flash was examined in rod photoreceptors of the larval-stage tiger salamander (Ambystoma tigrinum). Using suction electrodes, photocurrent responses to brief flashes were recorded from single, isolated rods in the presence and absence of steady background illumination. Background light decreased the saturation period (T) measured at fixed flash intensity (fixed If) and in this respect light-adapted the saturating response. Effects of the background on responses to weak (i.e. subsaturating) and bright flashes were compared with changes in a parameter, where ΔT is the decrease in saturation period, and where TR* is the slope of the line that relates T and ln If in a given state of adaptation. Dark- and light-adapted responses to flash intensities and , respectively, exhibited similar absolute peak photocurrent and falling-phase kinetics when and satisfied the relation, , where Ib is the background intensity. It is argued that ψ approximates the relative PDE*/R* gain of transduction, i.e. the relative peak level of activated cGMP phosphodiesterase (PDE*) produced by a given, small amount of photoactivated visual pigment (R*). Interpreted on this view, the results imply that light adaptation derives largely from a decrease in PDE*/R* gain, rather than from the stimulation of guanylate cyclase activity. The data are consistent with the possibility that modulation of the lifetime of PDE* underlies the background dependence of ψ.

scholarly journals Kinetics of Recovery of the Dark-adapted Salamander Rod Photoresponse

1998 ◽  
Vol 111 (1) ◽  
pp. 7-37 ◽  
Author(s):  
S. Nikonov ◽  
N. Engheta ◽  
E.N. Pugh
Keyword(s):  
Theoretical Analysis ◽  
Time Constant ◽  
Translation Invariance ◽  
Flash Intensity ◽  
Translation Invariant ◽  
Calcium Dependent ◽  
The Difference ◽  
Analytical Expressions ◽  
Kinetics Of ◽  
Flash Response

The kinetics of the dark-adapted salamander rod photocurrent response to flashes producing from 10 to 105 photoisomerizations (Φ) were investigated in normal Ringer's solution, and in a choline solution that clamps calcium near its resting level. For saturating intensities ranging from ∼102 to 104 Φ, the recovery phases of the responses in choline were nearly invariant in form. Responses in Ringer's were similarly invariant for saturating intensities from ∼103 to 104 Φ. In both solutions, recoveries to flashes in these intensity ranges translated on the time axis a constant amount (τc) per e-fold increment in flash intensity, and exhibited exponentially decaying “tail phases” with time constant τc. The difference in recovery half-times for responses in choline and Ringer's to the same saturating flash was 5–7 s. Above ∼104 Φ, recoveries in both solutions were systematically slower, and translation invariance broke down. Theoretical analysis of the translation-invariant responses established that τc must represent the time constant of inactivation of the disc-associated cascade intermediate (R*, G*, or PDE*) having the longest lifetime, and that the cGMP hydrolysis and cGMP-channel activation reactions are such as to conserve this time constant. Theoretical analysis also demonstrated that the 5–7-s shift in recovery half-times between responses in Ringer's and in choline is largely (4–6 s) accounted for by the calcium-dependent activation of guanylyl cyclase, with the residual (1–2 s) likely caused by an effect of calcium on an intermediate with a nondominant time constant. Analytical expressions for the dim-flash response in calcium clamp and Ringer's are derived, and it is shown that the difference in the responses under the two conditions can be accounted for quantitatively by cyclase activation. Application of these expressions yields an estimate of the calcium buffering capacity of the rod at rest of ∼20, much lower than previous estimates.

scholarly journals THE FLICKER RESPONSE FUNCTION FOR THE TURTLE PSEUDEMYS

1939 ◽  
Vol 22 (3) ◽  
pp. 311-340 ◽  
Author(s):  
W. J. Crozier ◽  
Ernst Wolf ◽  
Gertrud Zerrahn-Wolf
Keyword(s):  
Flash Intensity ◽  
Rods And Cones ◽  
Sensory Effects ◽  
Retinal Rods ◽  
Fixed Proportion ◽  
Order Of Magnitude ◽  
The Mean ◽  
Probability Integral ◽  
The Individual ◽  
Critical Intensity

1. At constant temperature, with a fixed proportion of light time in a flash cycle (namely, tL/tD = 1), the mean critical intensity for motor response to visual flicker by the turtle Pseudemys scripta follows a probability integral (log I) as a function of flash frequency F. The fit is close and satisfactory; certain quite minor but consistent deviations are adequately explained by features of the experiments. 2. The variation (σI) of critical I is directly proportional to the mean critical intensity (Im), over the entire explorable range. 3. These facts are consistent with the fact that the retina of this turtle is devoid of rods. It contains only cones, histologically, which, with their central representations, provide a single population of sensory effects. The properties of this population are compared with those of homologous populations deduced from corresponding measurements with other forms (various fishes; amphibian; man) which exhibit two such groups of sensory effects associated with the possession of retinal rods and cones. 4. Certain other formulations which have previously been applied to homologous data obtained with other organisms do not properly describe the Pseudemys measurements. 5. The use of a probability integral to describe the data of response to visual flicker for the dissection of the compound curves provided by animals possessing both rods and cones, is accordingly Justified. 6. Persisting differences among individuals of Pseudemys as regards the values of the critical flash intensity under various conditions of experimentation are of the same order of magnitude as are the transitory differences found in lots of other kinds of animals. 7. Determinations of mean critical flash frequency (Fm) at fixed levels of I lie slightly above determinations of Im at fixed values of I, as with other forms. The variation of critical flash frequency goes through a maximum as log I is increased; its height is lower than with certain other forms, in correlation with the low general slope of the F - log I curve (more properly, band). 8. These facts are consistent with the view that the dispersions of the individual critical intensities (and flash frequencies) are determined by organic variation rather than by "experimental error." 9. When the temperature is altered the F - log Im curve is shifted, with no change of Fmax. or of shape; the curve moves to lower intensities as the temperature is raised. 10. The reciprocal of the mean critical intensity, at fixed flash frequency, is a measure of excitability. With increase of temperature (12.5° to 36°) 1/Im for given F follows the Arrhenius equation, exhibiting a "break" at 29.5° (µ = 26,700, 12.5° to 29.5°; 12,400, 29.5° to 36°). This is explained by the necessary theory that, the number of elements of sensory effect required for the index response at fixed F being constant, the ease of their excitation is governed by temperature through its control of the velocity of an interrelated system of catalyzed processes common to all of the sensory elements concerned.

Properties of light adaptation in retinal rods

1992 ◽  
Vol 55 ◽  
pp. 71
Author(s):  
L. Cervetto ◽  
S. Bisti ◽  
A. Campagni ◽  
S. Del Bianco ◽  
G.C. Demontis ◽  
...  
Keyword(s):  
Light Adaptation ◽  
Retinal Rods

scholarly journals Novel Form of Adaptation in Mouse Retinal Rods Speeds Recovery of Phototransduction

2003 ◽  
Vol 122 (6) ◽  
pp. 703-712 ◽  
Author(s):  
Claudia M. Krispel ◽  
Ching-Kang Chen ◽  
Melvin I. Simon ◽  
Marie E. Burns
Keyword(s):  
Dark Current ◽  
Bright Light ◽  
Ambient Light ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Electrophysiological Recordings ◽  
Bright Flash ◽  
Retinal Rods ◽  
Rate Limiting ◽  
Flash Response

Photoreceptors of the retina adapt to ambient light in a manner that allows them to detect changes in illumination over an enormous range of intensities. We have discovered a novel form of adaptation in mouse rods that persists long after the light has been extinguished and the rod's circulating dark current has returned. Electrophysiological recordings from individual rods showed that the time that a bright flash response remained in saturation was significantly shorter if the rod had been previously exposed to bright light. This persistent adaptation did not decrease the rate of rise of the response and therefore cannot be attributed to a decrease in the gain of transduction. Instead, this adaptation was accompanied by a marked speeding of the recovery of the response, suggesting that the step that rate-limits recovery had been accelerated. Experiments on knockout rods in which the identity of the rate-limiting step is known suggest that this adaptive acceleration results from a speeding of G protein/effector deactivation.

scholarly journals Onset of Feedback Reactions Underlying Vertebrate Rod Photoreceptor Light Adaptation

1998 ◽  
Vol 111 (1) ◽  
pp. 39-51 ◽  
Author(s):  
Peter D. Calvert ◽  
Theresa W. Ho ◽  
Yvette M. LeFebvre ◽  
Vadim Y. Arshavsky
Keyword(s):  
Guanylate Cyclase ◽  
Light Adaptation ◽  
Continuous Illumination ◽  
Enzymatic Reactions ◽  
Rod Photoreceptor ◽  
Cgmp Phosphodiesterase ◽  
Rhodopsin Kinase ◽  
Slow Dissociation ◽  
Kinetics Of ◽  
Flash Response

Light adaptation in vertebrate photoreceptors is thought to be mediated through a number of biochemical feedback reactions that reduce the sensitivity of the photoreceptor and accelerate the kinetics of the photoresponse. Ca2+ plays a major role in this process by regulating several components of the phototransduction cascade. Guanylate cyclase and rhodopsin kinase are suggested to be the major sites regulated by Ca2+. Recently, it was proposed that cGMP may be another messenger of light adaptation since it is able to regulate the rate of transducin GTPase and thus the lifetime of activated cGMP phosphodiesterase. Here we report measurements of the rates at which the changes in Ca2+ and cGMP are followed by the changes in the rates of corresponding enzymatic reactions in frog rod outer segments. Our data indicate that there is a temporal hierarchy among reactions that underlie light adaptation. Guanylate cyclase activity and rhodopsin phosphorylation respond to changes in Ca2+ very rapidly, on a subsecond time scale. This enables them to accelerate the falling phase of the flash response and to modulate flash sensitivity during continuous illumination. To the contrary, the acceleration of transducin GTPase, even after significant reduction in cGMP, occurs over several tens of seconds. It is substantially delayed by the slow dissociation of cGMP from the noncatalytic sites for cGMP binding located on cGMP phosphodiesterase. Therefore, cGMP-dependent regulation of transducin GTPase is likely to occur only during prolonged bright illumination.

Effect of Isobutylmethylxanthine and Related Drugs on the Receptor Response (ERG; a-Wave) of the Frog Retina at Various Extracellular Calcium Concentrations

1981 ◽  
Vol 36 (7-8) ◽  
pp. 597-603 ◽  
Author(s):  
Karl H. Leser
Keyword(s):  
Cyclic Nucleotides ◽  
Calcium Concentration ◽  
Light Adaptation ◽  
Control Level ◽  
Ringer Solution ◽  
Extracellular Calcium ◽  
Response Amplitude ◽  
Time To Peak ◽  
Rod Cells ◽  
Frog Retina

Abstract Various drugs known or expected to increase the levels of cyclic nucleotides in cells were applied to isolated superfused frog retinae, and their influence on the aspartate-isolated a-wave was studied. Isobutylmethylxanthine (IBMX), triacetylguanosine (TAG), and dimethylaminopurine (DAMP) strongly influenced the responses elicited from dark-adapted retinae by flashes of light With all three drugs the response amplitude was increased, and latency and time to peak were prolonged. If, on the other hand, the retinae were light-adapted by background light of various intensities, the drugs showed different effects on the response amplitude: IBMX either did not influence the amplitude at all or even caused a decrease (4 of 6 experiments), DAMP decreased the amplitude and TAG caused an increase of the amplitude in 2 of 3 experiments. But latency and time to peak were still prolonged by all three drugs. When dark-adapted retinae were superfused with IBMX or TAG Ringer solution and simul­ taneously calcium concentration was raised, different effects of calcium on the three measured parameters of the a-wave were observed: By increasing the extracellular calcium concentration the increase of the amplitude caused by the drugs was reversed, down or even below the control level, whereas latency and time to peak remained prolonged. Thus, both an increased calcium level and light adaptation had the same effect, namely to reverse only that part of the drug effect concerning the amplitude but not latency or time to peak of the response. The data suggest that calcium and cyclic nucleotides act through different ways in the rod cells.

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