Recovery of cone receptor activity in the frog's isolated retina

Vision Res. Vol.

13. pp. 1943-1951.

RECOVERY

Pergaa~on

Press

1973.

Rintcd

in Grert

Briuis.

OF CONE RECEPTOR ACTIVITY FROG’S ISOLATED RETINA

IN THE

DONALDC. HOOD and PEGGY ANN HOCK Dept. of Psychology, Columbia University, New York, N.Y. 10027, U.S.A. (Receiced 13 March 1973)

study examines dark adaptation of the frog’s cones by recording sodium aspartate isolated receptor potentials from the frog’s isolated retina. FURUKAWAand HANAWA(1955) first showed that replacing part of the chloride in Ringer’s solution with aspartate suppresses PII of the ERG but leaves a stable PIII. Since it is known that PIII of the vertebrate retina has a dista1 and a proximal component (MURAKA;MI and KANEKO, 1966) it remained for SILLMAN,ITO and TOMITA (1969) to show that aspartate eliminates proximal PIII, leaving unaffected the receptor response, dista1 PIII. WITKOVSKY, NELSONand RIPPS (1973) have shown that a long latency, slow potential of nonreceptor origin remains after aspartate treatment. However the early portion of the response, including the initial amplitude, is generated in the receptor layer. Recently, CERVETTOand MACNICHOL(1972) recorded intracellularly from turtle cones and demonstrated that aspartate eliminates the effects of horizontal feedback leaving an apparently unaltered receptor response. The term “isolated retina” is used to designate a retina freed from the pigment epithelium and removed from the eye. Because the pigment epithelium is absent, little or no red rod pigment, rhodopsin, regenerates in the isolated retina (IWHNE, 1879; ZEWI, 1939; BAUMANN,1965; GOLDSTEIN,1967) except when the bleaching procedure involves long duration, short-wave light (FRANK, 1969; BAUMAXN,1970). However, ERP recording (GOLDSTEIN,1967, 1970) indicates that 80-90 per cent of the cone pigment with a X,,, at 580 nm (580 pigment) is regenerated in the frog’s isolated retina. If the 580 cone pi,gment regenerates in the frog’s isolated retina it is reasonable to expect the receptor potential of the 580 cone to recover sensitivity. HOOD and MASSFIELD(1972) recorded Na aspartateisolated receptor potentials before and after lights that bleached about 90 per cent of the frog’s rhodopsin. Although they found at least two receptor types recovering their sensitivity in the dark, there was a permanent loss in sensitivity to al1 wavelengths of stimulation. The fact that the loss was 1.36 log units greater at 487 nm than at 630 nm is consistent with Goldstein’s proposed 580 pigment regeneration. Since Hood and Mansfield did not have a good estimate of dark-adapted cone sensitivity owing to the greater sensitivity of the rods to al1 wavelengths in the dark, they could not estimate the extent of 580 cone recovery. In the present study we obtain a measure of the dark-adapted sensitivity of the 580 cones and then demonstrate that they recover nearly al1 their sensitivity following extensive light adaptation. THE

METHODS Stimulation Stimulation of the isolated retina was controlled by a two-channel projection system. All background and test lights uniformly covered the entire retina. The light source for this system was a 45 W quartz-iodide tungsten filament lamp operated at 6.6 A. The wavelength of stimulation was controlled by Baird-Atomic 1943

1944

DONALD

C. HCXXD ASD PEGGYA>Y HOCK

interferente fìlters. These filters were calibrated with a spectrophotometer and had half-band widths of 6-9 nm. Intensities were controlled by neutra1 density flters. The relative energies at the retina for these interferente and neutra1 density filters were calibrated using an EG&G radiometer. Exposure duration was controlled by a solenoid shutter. Al1 test stimuli were 50 msec in duration. Adap ring ligh t

The spectral composition of the unfiltered adapting light was measured by placing a spectral radiometer in the plane of the retina. This spectral composition was best fitted by a black body curve for 2400°K. This spectral output will be referred to below as white light. Using an SEI photometer and a test piate from a MacBeth Illuminometer positioned where the retina would normally be, the maximum illuminante on the retina for the white light was determined to be 237 ft-cd. The adapting light for experiment 1 was the full intensity white light passed through Coming filter 3-72 which cuts off 50 per cent of the light at 438 nm and 99 per cent at 430 nm. Wben the ultraviolet light is eliminated from the bleaching light no detectable rhodopsin regeneration occurs in the frog’s isolated retina (FRASK, 1969). The full intensity adapting light was found to bleach 88 per cent of the rhodopsin (HOOD, HOCK and GROVER,1973). It was estimated that this light bleached most of the 580 cone pigment.’ Preparation

Frogs (Rana pipiens) about 2.5 in. in body length were used for these experiments. Frogs were dark adapted for a minimum of 24 hr. A dark-adapted frog was decapitated and one of its eyes enucleated. The anterior portion of the eye was removed by cutting below the ora serrata with iridectomy scissors. The retina was carefully teased away from the pigment epithelium in a dish of Na aspartate Ringer’s solution. The solution was made according to FURUKAWAand HANAWA’S(1955) norma1 Ringer’s with 15 rn%f Na aspartate replacing 15 rn>f NaCI. The retina was then floated, receptors down, onto a cotton pad soaked in Ringer’s solution. This entire procedure was perfonned under deep red light (Corning Filter 2-60) to insure that no rhodopsin would be bleached. The cotton pad with the isolated retina was placed in a plastic chamber. This chamber, similar in principle to that of MACNKHOL and SVAETKHIN(1958), had a moat filled with Ringer’s solution surrounding, but not touching, the retina. Oxygen flowed slowly into the chamber, creating a moist, oxygenated atmosphere. The retina in both the recording and bleaching apparatus was at room temperature, between 20 and 24°C. Recording system

Ringer-soaked cotton wick electrodes in contact with Ag-AgCl wire were connected to the differential input leads of a low leve1 preamplifier (Tektronix type 122). The output of the preamplifier was connected to an oscilloscope (Tektronix type 502A). The low frequency cutoff of the preamplifier was set at 0.2 Hz and the high frequency cutoff at 50 Hz. The records of Figs. 1 and 2 were repeated with an Argonaut type LAR preamplifier with cutoffs set at @02 and 250 Hz to assess the effects of the 0.2 and 50 Hz cutoffs. The cone responses were identica]. The slow potentials in Figs. 1 and 2 were virtually identica1 at 10 PV but curtailed with increased intensity. The Tektronix preamplifìer was used for the rest of the experiments since the results are identica1 and the signal-to-noise ratio far superior. The wick of one electrode, the referente, was placed under the cotton pad and the wick of the other,

the recording electrode, was allowed to just touch the surface of the retina. PROCEDURE

AND

RESULTS

Experiment 1. Cone sensitivity in the dark-adapted retina In order to measure the extent of recovery of cone sensitivity during dark adaptation of the isolated retina, it was first necessary to determine the sensitivity of the cones in the darkadapted retina. This is not a trivial problem since the rods are more sensitive than the cones regardless of the wavelength of stimulation. However, the dark-adapted cone sensitivity can be measured by taking advantage of the markedly different waveforms for the rod and cone responses and the fact that the 580 cone is the only receptor in the frog retina having a visual pigment with a Amaxgreater than 502 nm. ’ A retina1 illumination of 237 ft-cd is equivalent to 7.21 x lo5 td (WESTHEIMER,1965) and bleaches greater than 90 per cent of human cone pigment (RG’SHTON,1963). Since (a) the frog’s 580 cone pigment regenerates more slowly and (b) the spectral distribution of the adapting light is more effettive for the frog’s 580 cones than for human cones, then this adapting light should be bleaching most of the 580 cone pigment. Note added in proofi We have recently used ERP amplitude (see GOLDSTEIN,1968) to measure the 580 cone pigment content. The adapting light is bleaching greater than 90 per cent of the 580 pigment.

Recovery of Cone Receptor Activity in the Frog’s Isolated Retina

10-4

intensity

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501 nm

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630nm

intensity

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2.71

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FIG. 1. A procedure for estimating the intensity of a 630 nm flash necessary to evoke a 10 PV criterion cone response. Sample responses presented were evoked by 501 and 630 nm lights of threshold intensity (i.e. intensity necessary to produce a 10 PV response) and intensities 0.62 and 0.92 log unit above threahold level. A 0.0 log intensity corresponds to 0.93 log quanta/ sec. Pm-’ (- 0.37 log quantalflash . Pm-‘). The responses to the 630 nm light are traced as the dashed curves onto the “corresponding responses” to 501 nm light. These corresponding responses are evoked by lights of equa1 rod effectiveness. The differente in response shape must be due to 580 cone activity. See text for details.

630

No

nm

background

501 nm

n FIG. 2. Five responses to a 630 nm, 50 msec flash of 2.06 log quanta/0ash.pm-2 One flash was presented in the dark and the other four on steady backgrounds intensity of 501 nm light. V.S.

13/1&E

are shown. of increasing

DOX~LD C. HOODAW PEWSY Ahi HOCK

1946

After the isolated retina was placed in the experimental chamber its sensitivity was monitored by adjusting the intensity of 50 msec, 501 and 630 nm flashes such that 10 PV responses were evoked. Figure 1 (row 1) presents sample 10 PV responses taken after sensitivity had stabilized. In agreement with HOODand MANSFIELD (1972), the two responses show identica1 waveforms and the relative sensitivities expected from a 502 nomogram pigment adjusted for a density of O-75, the density of the frog rod pigment (LIEBMAXand E~n-n, 1968). It is therefore likely that both these responses are generated by the red rods. The records in the second and third rows are responses to flash intensities increased by about 0.6 and 0.9 log unit above the intensities necessary for the 10 PV responses. Each pair of monochromatic stimuli should be equivalent intensities for the rods but the 630 nm light t. mi”

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20 Time,

25

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30

35

I

40

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FIG.3. Log relative threshold intensity of a 630 nm, 50 msec test flash necessary to elicit a 10 PV re-spanse as a function of time foliowing 5 min of an intense adapting light. Each curve represents a single preparation. The curves are adjusted SOthat 0.0 log threshold intensity represents the preadaptation cone threshold for each preparation. The sample records are of near threahold responses (i.e. about 10 PV) and the entire trace represents 2 sec.

should be about l-97 log units more effettive for the 580 cones (see Fig. 3). Therefore, if the receptor potentials in Fig. 1 are merely algebraic summations of rod and cone responses the differente between paired stimuli can be taken as the 580 cone response. The responses to the 630 nm flash have been traced onto the corresponding responses to the 501 nm flash. Note that the fast component increases with increased intensity. The peak differente between the 501 and 630 nm responses is about 14 PV at the intermediate intensity and about 25 PV at the highest intensity, nearly doubling with doubling light intensity. If we are correct in attributing the short latency response to a 580 cone and the slow, prolonged response to the 502 rod then we should be able to adapt these two components selectively. Figure 2 shows a series of records from the same preparation recorded in response to 630 nm flashes. The intensity of the 630 nm flash was set at 2.43 log umts (see Fig. 1). The top record in Fig. 2 shows a sample response without a background present. The successive records indicate the effect of increasing the intensity of a steady 501 nm background. Note that the slow component is decreased leaving the fast component

Recovery of Cone Receptor Activity in the Frog’s Isolated Retina

1947

attributed to the 580 cone. More important, the amplitude of 15 PV is close to the measurement obtained from Fig. 1 by subtracting. We conclude that we are able to estimate the sensitivity of the dark adapted 580 cones before bleaching either by subtraction (Fig. 1) or by selettive adaptation (Fig. 2). On the average we record a 10 PV cone response to a 50 msec 630 nm light when the intensity of this light is 3.42 log quanta/sec .pm -* (2.12 long quanta/flash.pm-*). Assuming a base diameter of 3 Pm, an optical density at h,, of 0.20, and the relative absorption spectrum al1 given by LIEBMAN and ENTINE(1968), then a flash intensity of 2.12 log quanta/flash . prne2 is calculated to result in 105 quanta absorbed/flash per cone. Taking into account the 5 : 3 ratio of rods to cones the cone Signa1 we record per quanta absorbed is seven times smaller than the rod Signa1 we record per quanta absorbed by the rods (HOOD, HOCK and GROVER, 1973).’

Experiment 2. Recovery of cone sensitivity The procedures in experiment 1 were employed to estimate the dark-adapted 580 cone threshold for each retina. Following these procedures the preparation was exposed to the 5 min adapting light. The recording electrode was removed before adaptation and replaced with 30 sec remaining. The sensitivity of the preparation was then monitored during dark adaptation by adjusting the intensity of the 630 nm test flash such that a 10 PV response was obtained. Flashes were given at 30 sec intervals during the first 3 min of dark adaptation and every minute thereafter. Figure 3 shows the recovery of sensitivity in the dark of three preparations. Note that immediately after light adaptation the threshold is substantially elevated and over the next 30 min retums close to the dark adapted leve1 (0.0 log threshold intensity). The average sensitivity of nine retinas following 30 min of dark adaptation was only 0.16 log unit (S.D. = 0.12) lower than the origina1 dark-adapted cone sensitivity. Note that the responses obtained after 30 min of dark adaptation closely resemble the dark-adapted cone responses shown in Figs. 1 and 2. The response waveforms, relative spectral sensitivities, and the results of experiment 3 argue that the entire recovery curves in Fig. 3 are controlled by the 580 cones. Exponential curves were fitted by computer program to the log threshold data points for each preparation. The obtained haif-times and r* are: 3.8 min (rz = 0.993); 4.9 min (O-992); and 7.8 min (0.986). Experiment 3. The short-latency response is generated by a receptor with a 580 nm pigment

A variation of Stiles’ two-color threshold technique (STILES, 1959) previously employed electrophysiologically (BURKHARDT, 1968) was used to determine the receptor controlling the response to a 630 nm test flash following a 5 mm adapting light and 50 min of dark adaptation. The intensity of the 630 nm test flash was increased unti1 a 20 PV response was obtained. Homogeneous backgrounds of monochromatic lights (430, 460, 487, 521, 542, 580 and 630 nm) were presented and the intensity was determined for each that would decrease the response to the superimposed 630 rm~ flash to 10 ,uV. The 630 nm flash was presented every minute. On alternate minutes one monochromatic background of a Gxed 2 This rod-cone comparison should be viewed with some skepticism since it is based on numerous estimates: receptor dimensions, relative number of rods and cones, pigment absorption, etc. In addition, the cones in the isolated retina may not be SO well oriented toward incoming quanta as the cones in the intact frog. This could lead to a decrease in number of quanta absorbed (Stiles-Crawford effect).

1948

DONALD

C.

HOOD

AND

PEGGY

A~X HocK

intensity was turned on 15 sec before the flash and turned offa few seconds after it. The test flashes on the alternate minute without a background present served to ensure that the preparation had retumed to its stabie sensitivity. Using this procedure two intensities were found for each monochromatic background that resulted in 630 nm test flash responses that bracketed the 10 PV criterion. The intensity necessary to elicit a criterion response was interpolated from these values.

Waveien~~,

flm

reciprocairelativenumber of quanta (Le. log relativequanta1sensititity) necessaryin a steady monochromaticbackground Iight to decreasethe response to a 630 nm test flash from 20 @Vto 10 pV is plotted as a function of the wavelengthof the background of light. The two retinas used in the experiment are denoted by different symbols. The relative FIG. 4. The log of the

position of the set of data points for each preparation was adjusted to minimize the squared deviation among points [O-O5log unit (M) and 0.05 log unit (O)]. The dashed Iine represents the log of the relative absorption for the frog’s 580 cone pigment as measured by LIEBMAN and ENI-NE(1968) using microspectrophotometry. The continuous line is an estimate of the absorption spectrum of 580 conca obtained from Goldstein’s ERP data [GOLD~TEN(1968, Fig. 3) presents action spectra for the ERP with and without an intense red background. Since the ERP amplitude is proportional to the number of quanta absorbed, an estimate of the absorption spectrum of the 580 cone is obtained by subtracting the quanta1 sensitivity against the red background from that in the dark. The logs of these differences are presented as the smooth curve.]

Figure 4 presents the resuìts from three preparations along with two estimates of the absorption spectrum for the frog’s 580 cone pigment. Plotted in this figure are the reciprocals of the intensities of the monochromatic backgrounds producing a constant adapting effect (i.e. reducing the response to 10 PV) on the response to 630 nm light. If we assume that the responses of the various receptor types in the aspartate-treated retina are independent (Le. the response of one receptor type does not infiuence the response of another) then these data points provide an estimate of the action spectrum of the receptor or receptors producing the response to 630 nm light. This assumption of independence is well supported by Figs. 1 and 2. Therefore, given the agreement to the 580 pigment curves and the lack of any evidente of a 502 receptor involvement it seems reasonable to conclude that the 580 cones produce the short-latency response to 630 nm light.

Recovery of Cone

Receptor Activity in the Frog’s Isolated Retina

1949

DISCUSSION In the frog’s isolated retina, without the presente of the pigment epithelium, GOLDSTEIN (1970) showed that the ERP generated by the 580 cones recovered 80-90 per cent of its amplitude following extensive light adaptation. Since the amplitude of the ERP is directly proportional to the number of unbleached pigment molecules (CONE,1964; CONEand COBBS, 1969), this recovery of ERP amplitude argues for 80-90 per cent regeneration of the 580 cone pigment. In the present study, the sensitivity of the 580 cone receptors recovered nearly al1 their sensitivity after an extensive bleach. In experiment 1 the sensitivity of the dark-adapted cones was estimated. The short-latency potentials we recorded have very similar latencies and waveforms to those recorded intracellularly in turtle cones by BAYLOR,FOURTESand O’BRIEN(1971). The results of experiments 1 and 2 argue that our recordings are not only from cones but from the frog’s 580 cones. The 580 cones comprise about 30 per cent of the frog’s receptors (LIEBMANand ENTINE, 1968). Since the 580 cone is the only receptor containing a pigment with a h,,, greater than 502 nm, experiment 1 strongly argues for 580 cone contro1 of the short-latency response. In addition, experiment 3 (Stiles technique) indicates that this short-latency response to 630 nm light is indeed controlled by a receptor with a 580 pigment. Experiment 2 determined that the frog’s 580 cones recover nearly al1 their sensitivity after extensive bleaches. Interestingly, the log of the receptor sensitivity is recovering with an average half-time of 5.4 min, close to Goldstein’s ERP recovery half-time (5-6 min). At the leve1 of the frog’s cones the log of receptor sensitivity appears to parallel recovery of cone pigment. This is the same correlation that is seen between human cone pigment and psychophysically measured cone system sensitivity (RUSHTON,1965). The following paper demonstrates that unlike the 580 cones, the 502 rods permanently lose much of their sensitivity with extensive pigment bleaching. However, the rods and cones may show the same permanent loss in sensitivity per percentage pigment bleached. If we assume that 580 cone pigment is regenerating to the same extent in our study as it did in Goldstein’s, then the cones have permanently lost about 0.16 log unit in sensitivity when IO-20 per cent of their pigxnent has been bleached. Compare to this the rods permanent loss of about 0.15 log unit for a permanent bleach of 10 per cent (HOOD, HOCK and GROVER, 1973). Acknowfedgements-This research was supported by a grant from the Institutional Scientific Research Pool of Columbia University. We are gratefui to Drs. E. B. GOLDSTEIN and J. GORDONfor their helpful comments on this manuscript and to Dr. B. A. SCHNEIDERfor his time and the computer program used to fit the exponential curves in experiment 3. Finally, we thank Dr. E. GALAK~ERfor makiog available the facilities of his laboratory which are supported in part by a contract with the Office of Nava1 Research. REFERENCES BAUMANN,CH. (1965). Die Photosensitivitat des Sehpurpurs in der isolierten Netzhaut. Vision Res. 5, 425-434. BAUMANN,CH. (1970). Regeneration of rhodopsin in the isolated retina of the frog (Rana esculento). Vision Res. 10,627-637. BAYLOR,D. A., Fouarss, M. Ci. F. and O’BRYAN,P. M. (1971). Receptive fields of cones in the retina of the turtle. J. Physiol., Lmd. 214, 265-294. BLJRKHARDT, D. A. (1968). Cone action spectra: evidente from the goldfkh electroretinogram. Vision Res. 8,839-853. CERRETTO,L. and MACNICHOLJR., E. F. (1972). Inactivation of horizontal cells in the turtle retina by glutamate and aspartate. Science, N. l’. 178, 767-768. CONE, R. A. (1964). Early receptor potential of the vertebrate retina. Nume. Lond. 204, 736-739.

D~NALD

1950

C. HOOD AND PEGGYANN HOCK

CO‘IE, R. A. and COBBS,W. H. (1969). Rhodopsin cycle in the living eye of the rat. ,Vuntre, Lo&. 221, 820--822. FRANK, R. N. (1969). Photoproducts of rhodopsin bleaching in the isolated, perfused frog retina. Visiou Res. 9, 1415-1433. FURUKAWA,T. and HANAWA,1. (1955). Effects of some common cations on electroretinogram of the toad. Jap. J. Physiol. 5.289-300.

GOLDSTEIN,E. B. (1967). Early receptor potential of the isolated frog (Rana Pipiens) retina. Vision Res. 7, 837-845.

GOLDSTEIN,E. B. (1968). Visual pigments and the early receptor potential of the isolated frog retina. Vision Res. 8, 953-964.

GOLDSTEIN,E. B. (1970). Cone pigment regeneration in the isolated frog retina. Vision Res. 10, 1065-1068. HOOD, D. C., HOCK, P. A. and GRO~ER, B. G. (1973). Dark adaptation of the frog’s rods. Vision Res. 13, 1953-1963. Hood, D. C. and MANSF~ELD, A. F. (1972). The isolated receptor potential of the frog: action spectra before and after extensive bleaching. Yjsjotr Res. 12, 2109-2119. KUHNE, W. (1879). Chemische Vorgange in der Netzhaut. In Handbuch der Physiologischen. (edited by L. HERMANN),Vol. 3, 235-342. LIEBMAN,P. A. and ENTINE, G. (1968). Visual pigments of frog and tadpole (Rana Pipiens). Vision Res. 8, 761-775. MACNICHOL, E. F., Jr. and SVAETICHIN,G. (1958). Electric responses from the isolated retinas offishes. Am. J. Physiol. 46, 26-40.

MURAKAMI,M. and KANEKO,A. (1966). Differentiation of PII1 subcomponents in cold-blooded vertebrate retinas. Vision Res. 6, 627-636. RUSHTON, W. A. H. (1963). Cone pigment kinetics in the protanope. J. Physiol., Lond. 168, 374-388. RUSHTON, W. A. H. (1965). Cone pigment kinetics in the deuteranope. J. Physiol., Lond. 176, 38-45. SILLMAN, A. J., ITO, H. and TOMITA,T. (1969). Studies on the mass receptor potential of the isolated frog retina. 1. General properties of the response. Vision Res. 9, 1435-1442. Snrzs, W. S. (1959). Color vision: the approach through increment-threshold sensitivity. Proc. nat. Acad. Sci., Wash. 45, 100-114. WESTHEIMER,G. (1965). The maxwellian WITKOVSKY, P., NELTON, J. and RIPPS,

view. Vision Res. 6, 669-682. H. (1973). Spectral properties of the isolated receptor potential of

the carp retina. J. gen. Physiol. 61, 401-423. ZEWI, M. (1939). On the regeneration of visual purple. Atta SOC.Sci. finn. N.S.B. 2, l-57.

Abstract-Using sodium aspartate Ringer’s we recorded gross potentials from the receptors of the frog’s isolated retina. With appropriate selection of stimulating conditions, dark adaptation of the 580 cones was studied. After intense lights that bleach substantial cone pi_went and raise cone threshold over 2 log units, the cones recover nearly al1 their sensitivity, within 0.16 log unit. This is in marked contrast to the 502 rods (see foliowing paper) and is consistent with Goldstein’s ERP evidente that indicates 580 cone pigment regeneration in the isolated retina.

Résum&On enregistre les potentiels de masse des récepteurs de la retine isolée de grenouille par une solution de Ringer B l’aspartate de sodium. On étudie I’adaptation B l’obscurité des canes 580 par un choix appropri6 des conditions de stimulation. Après une lumière intense qui decolore nettement le pigment des cònes et Cleve leur seuil de plus de 2 unités log, les cones récupèrent presque toute leur sensibilité à mieux que 0.16 unité log. C’est en opposition marquée avec les batonnets 502 (voir article suivant) et en accord avec le résultat d’ERP de Goldstein qui indique une régénération du pigment de cone 580 dans la retine isolee.

Zusammenfassung-In einer Ringer-Losung, die mit Na-aspartat versetzt war, wurden grobe PotentiaIe aus den Rezeptoren der isolierten Froschnetzhaut aufgenommen. Durch geeignete Wahl der Reizbedingungen konnte die Dunkeladaptation des Zapfenpigrnents bei 580 nm untersucht werden. Nachdem intensives Licht das Zapfensigment ausbleichte und die Schwelle um 2 logarithmische Einheiten erhohte, gewannen die Zapfen ihre urspt%ngliche Empfindlichkeit innerhalb 0,16 logarithmischen Einheiten fast wieder. Das steht im Gegensatz zur Untersuchung bei Stàbchenpigrnenten bei 502 nm (vergl. die folgende Veroffentlichung) und stimmt mit der Aussage Goldsteins Liber das ERP fiberein, wonach sich das Zapfenpigment bei 580 nm in der isolierten Retina regeneriert.

Recoveryof Cone ReceptorActivity in theFrog'sIsolated Retina

1951

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