Decreased energy requirement of toad retina during light adaptation as demonstrated by 31P nuclear magnetic resonance.

Apte, Dipali V.; Ebrey, Thomas G.; Dawson, M. Joan

doi:10.1113/jphysiol.1993.sp019635

Cited by 8 publications

(5 citation statements)

References 30 publications

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“…For this rod outer segment, the pH in the band was 7.30, whereas the pH in the rest of the outer segment (diffuse staining) was 7.11. Overall, the cytoplasmic pH was 7.29 Ϯ 0.02 (n ϭ 27) in good agreement with 31 P-nuclear magnetic resonance measurements (Apte et al, 1993), whereas intradiskal BCECF reported a pH of 6.50 Ϯ 0.07 (n ϭ 35) ( Fig. 6 c).…”

Section: Table 1 Apparent Diffusion Coefficients For Different Tracerssupporting

confidence: 80%

Dynamic Behavior of Rod Photoreceptor Disks

Chen

Yun-Hai

Koutalos

2002

Biophysical Journal

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Eukaryotic cells use membrane organelles, like the endoplasmic reticulum or the Golgi, to carry out different functions. Vertebrate rod photoreceptors use hundreds of membrane sacs (the disks) for the detection of light. We have used fluorescent tracers and single cell imaging to study the properties of rod photoreceptor disks. Labeling of intact rod photoreceptors with membrane markers and polar tracers revealed communication between intradiskal and extracellular space. Internalized tracers moved along the length of the rod outer segment, indicating communication between the disks as well. This communication involved the exchange of both membrane and aqueous phase and had a time constant in the order of minutes. The communication pathway uses approximately 2% of the available membrane disk area and does not allow the passage of molecules larger than 10 kDa. It was possible to load the intradiskal space with fluorescent Ca(2+) and pH dyes, which reported an intradiskal Ca(2+) concentration in the order of 1 microM and an acidic pH 6.5, both of them significantly different than intracellular and extracellular Ca(2+) concentrations and pH. The results suggest that the rod photoreceptor disks are not discrete, passive sacs but rather comprise an active cellular organelle. The communication between disks may be important for membrane remodeling as well as for providing access to the intradiskal space of the whole outer segment.

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Section: Table 1 Apparent Diffusion Coefficients For Different Tracerssupporting

confidence: 80%

Dynamic Behavior of Rod Photoreceptor Disks

Chen

Yun-Hai

Koutalos

2002

Biophysical Journal

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“…Those studies measured QO 2 by using an Oz balance within a closed chamber. The value of QO 2 for the entire retina in this study decreased in light to 55 % of the dark value, which was similar to the 43 % decrease found in the frog retina (Zuckerman and Weiter, 1980) and the 60% decrease estimated from intracellular ADP levels in the toad retina (Apte, Ebrey and Dawson, 1993). Calculating QO 2 from a PO 2 profile and a diffusion model has the advantage of uncovering spatial heterogeneities in retinal QO 2.…”

Section: Retinal Q02supporting

confidence: 86%

Oxygen consumption in the isolated toad retina

Haugh-Scheidt

Linsenmeier

Griff

1995

Experimental Eye Research

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Retinal 02 utilization was studied to identify the 02 consuming processes in the retina and the spatial distribution of those processes. Neural retina, retinal pigment epithelium and choroid were dissected from the toad eye and superfused with an oxygenated Ringer's solution. Double-barreled microelectrodes were used to measure 02 and local voltage simultaneously within the retina in both light and dark adaptation. The profile of PO 2 was measured during a withdrawal of the electrode tip across the retinal pigment epithelium and through the neural retina. The PO 2 decreased through the distal retina, reaching a minimum in the inner segment or outer nuclear layer, and then increased steadily through the proximal retina. From fitting PO 2 profiles measured in the dark-adapted retina to a three-layer diffusion model, 02 consumption was found to be 1"0+0"4 and 0'4+0-3 ml 02 (100 g min) -x in the outer and inner halves of the retina, respectively. Light decreased consumption in both halves of the retina. In steady illumination (500 nm) that saturated the ERG b-and c-waves, 02 utilization decreased significantly to 48 % and 68 % of the dark values in the outer and inner retina, respectively. When Na ÷ was removed from the superfusate to inhibit the photoreceptor Na+/K ÷ pump, 02 consumption in the outer retina decreased by about the same amount as in light, but Oz consumption in the inner retina was not significantly affected.

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“…Unless the rate of IBMX block were very fast, the Ca2" inhibition of the cyclase would have the effect that &Jmaxwould underestimate a', and the magnitude of this error should increase with increasing light intensity. Furthermore, the small decreases in [GTP] which have been observed in illuminated photoreceptors (Biernbaum & Bownds, 1985;Apte et al 1993) would cause a' to underestimate a.…”

Section: Assumptions Of the Methodsmentioning

confidence: 99%

“…If light or a solution change were to decrease the GTP concentration (see for example Biernbaum & Bownds, 1985), a' would underestimate the change in (5) cyclase velocity. This discrepancy is likely to be small (Dawis, Graeff, Heyman, Walseth & Goldberg, 1988;Apte, Ebry & Dawson, 1993).…”

Section: Theorymentioning

confidence: 99%

Bleached pigment activates transduction in isolated rods of the salamander retina.

Cornwall

Fain

1994

The Journal of Physiology

194

200

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1. We have used suction electrode recording together with rapid steps into Li' solution and 0 5 mM IBMX solution to estimate the rates of the guanylyl phosphodiesterase (PDE) and guanylyl cyclase in isolated rods of the salamander, Ambystoma tigrinum. 2. We show that both the PDE and cyclase velocities are accelerated by steady background light. The steady velocities of both enzymes appear to be saturating functions of background intensity. 3. Bleaching also accelerates both the PDE and cyclase. This effect is maintained long after the bleaching stimulus is removed (up to 2 h) and is reversed only if the photopigment is regenerated with exogenous chromophore. 4. The estimated steady-state PDE and cyclase velocities appear to be linear functions of the amount of pigment bleached, as if each bleached pigment molecule activated the transduction cascade with the same probability and gain. 5. The effectiveness of bleached pigment in activating transduction is only 10-6 to times that of activated rhodopsin (Rh*), but this is sufficient after large bleaches to produce an 'equivalent background' excitation of the rod, which is probably responsible, at least in part, for bleaching desensitization.When the eye is exposed to light bright enough to bleach a significant fraction of the visual pigment, the sensitivity of the visual system is greatly depressed and recovers slowly. This phenomenon, known as dark adaptation or bleaching adaptation, is still poorly understood. Since the recovery of sensitivity has a time course which is approximately the same as the regeneration of visual pigment (Rushton, 1965), it is reasonable to suppose that the loss of pigment is somehow responsible for the loss of sensitivity. However, it has long been realized that the decrease in sensitivity is much greater than would be expected from the decrease in the probablility of light absorption by the photopigment (Campbell & Rushton, 1955). The visual system appears to produce a bleaching signal that elevates threshold much more than simple loss of pigment would predict.To investigate the nature of this bleaching signal, we have recorded from isolated rods of the salamander, Ambystoma tigrinum. Earlier experiments have shown that the bleaching of pigment in these photoreceptors produces a loss of sensitivity which, like that in the visual system as a whole, is considerably greater than expected from the decrease in pigment concentration (Cornwall, Fein & MacNichol, 1990). Furthermore, the light responses of bleached rods at steady state have many of the characteristics of those of rods in the presence of background light: sensitivity is decreased, circulating current is reduced, and the decay time of the response to brief flashes is accelerated. These observations suggest that bleaching may desensitize the rods by producing an 'equivalent background' excitation, as first suggested from psychophysical experiments by Stiles & Crawford (1932).Furthermore, the similarity of responses in the presence of background light and after bleaches suggests t...

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Decreased energy requirement of toad retina during light adaptation as demonstrated by 31P nuclear magnetic resonance.

Cited by 8 publications

References 30 publications

Dynamic Behavior of Rod Photoreceptor Disks

Dynamic Behavior of Rod Photoreceptor Disks

Oxygen consumption in the isolated toad retina

Bleached pigment activates transduction in isolated rods of the salamander retina.

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