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Dark adaptation in the isolated rat retina
IUPS-ISCERG
Symposium Papers
1197
few hundred quanta incident per rod per second, or more, and the amplitude is related to the light intensity; (iii) after dim illuminations the efflux increases when the light is interrupted but this is less promptly than after strong illuminations; (iv)the whole effect is also seen when the retina is perfused with a physiological solution with 10 mM of sodium glutamate, a condition in which light flashes elicit a vitreous-negative electroretinogram only; (v) the amplitude of the effect is linearly related to the logarithm of the concentration of sodium ions in the perfusing solution. The effect presents physiological characteristics, but a retention of potassium ions during stimulation does not seem to fit in the general mechanisms of excitation of the nervous tissue.
13 Light adaptation in the cat retina B. SAKMANNand M. FILION. Biophysics. Dept. U.C.L. London, W.C.l. IN AN attempt to localize the site of light adaptation
within the cat retina, a comparison was made of the effect of background light on the late receptor potential and on the ganglion cell response. The increment threshold and the stimulus-response relation were measured for both types of responses in darkness, and at background illuminations of increasing intensity within the scotopic and mesopic range. The increment threshold of the late receptor potential is little affected by raising the background illumination to 7 x 1Om8 1 m/mm,’ whereas the increment threshold of the ganglion cell rises considerably. The intensity range of responses between increment threshold and saturation of the late receptor potential is approximately 4 l0log units of stimulus intensity in darkness. Background light decreases both the intensity range of the response and the maximal amplitude. For the ganglion cells the range of the stimulus-response relation between increment threshold and saturation is approximately 2 ,,Jog units of stimulus intensity at all background illuminations and the amplitude of the maximal response is independent of the background illumination. It is concluded that in the cat retina the site of light adaptation at scotopic and mesopic background illuminations is central to the rod receptors. REFERENCE SAKMANN,B. and CREUTZFELD, J. 0. D. (1969), Arch. ges. Physiol. 313, 168.
14 Dark adaptation in the isolated rat retina W. ERNST and C. M. KEMP. Dept. of Neurophysiology, Institute of Ophthalmology, London,
w.c.1 THE DARK
adaptation of the isolated albino rat retina has been studied, using parallel spectrophotometric and electroretinographic methods. A Ca2+ free perfusing medium containing EDTA was used to isolate the late receptor potential (PIII). After intense lightadaptation, the amplitude of the response (V) of PI11 to a stimulus of constant intensity grows sigmoidally, and continues to change for more than 50 min. at the temperatures used
1198
IUPS-ISCERG Symposium Papers
In contrast, the b-wave (WEINSTEIN, HOBS~Nand DOWLING,1967) and ganglion cell thresholds (WEINSTEINand HOB.SON,1970) stabilize within 10 min. The increase of PI11 ampiitude with time in the later single-exponential phase is the same as the rate of disappearance of metarhodopsin III (465). This correlation has been demonstrated at 24”, 29’ and 34°C. The change in sensitivity for a given bleach is much smaller for PI11 than for the b-wave. Approximately 50 % bleaches do not reduce V,, by as little as 20x, while the light intensity required to produce a given response increases tenfold. REFERENCES WEINSTEIN and HOBSON (1970).Nature, Lord 227, 957. WEINSTEIN, HOBS~Nand DOWLING,J. E (1967). Nature, Lord 215, 134.
15 Afterpotentials
in retinula ceils of the drone’
F. BAUMANNand B&NICE HADJILAZARO. Dept. Physiol. University of Geneva, Switzerland THE RJSTINULA cell of the honeybee drone responds to light by a depolarization of graded amplitude, the receptor potential, which may be followed by either a hyperpoiarizing or a depolarizing afterpotential (HADJILAZARO and BAUMANN,1968). During the hyperpolarizing afterpotential the membrane potential of the cell is greater than the resting or dark potential; during the depolarizing afterpotential it is less. Which of these two afterpotentials dominates the return to dark potential depends on the duration and the intensity of the preceding flash. Thus, the depolarizing afterpotential is most marked after strong stimuli giving rise to a receptor potential of maximum amplitude. The effects on the two afterpotentials of changes in the ionic composition of the bathing medium and of intracellularly applied polarizing currents, as well as measurements of the membrane resistance of the retinula cell, suggest that during the depolarizing afterpotential the membrane is in a state similar to that of the illuminated membrane. It thus appears that the process initiated by the absorption of light by the photopigment and which gives rise to the receptor potential, may continue to be effective for some time after the end of illumination. The hyperpolarizing afterpotential was found to be due, at least partially, to the activity of a pump which after a light flash pumps sodium out and potassium into the retinula cell. REFERENCE HADJILAZARO, B. and BAUMANN, F. (1968). Afterpotentials of the visual cell of the honey-bee drone. Helv. Physiol.Acta 26, CR 351. ’ This work was supported by grants from the Fonds National Suisse de la Recherche Scientifique and the Fondation Sandoz. 18 Damage to pigeon retinae by commercial l&t
sources operating at moderate levels
J. MARSHALL,J. MELLERIOand D. A. PALMER.Institute of Ophthalmology, Judd Street, London, W. C. 1 THE TOXIC action of moderate levels of light upon rat retinae has been reported in the literature. We wished to extend these observations to a retina with more typical rods and cones. We also intended to determine a threshold for damage related to commercial light
Symposium Papers
1197
few hundred quanta incident per rod per second, or more, and the amplitude is related to the light intensity; (iii) after dim illuminations the efflux increases when the light is interrupted but this is less promptly than after strong illuminations; (iv)the whole effect is also seen when the retina is perfused with a physiological solution with 10 mM of sodium glutamate, a condition in which light flashes elicit a vitreous-negative electroretinogram only; (v) the amplitude of the effect is linearly related to the logarithm of the concentration of sodium ions in the perfusing solution. The effect presents physiological characteristics, but a retention of potassium ions during stimulation does not seem to fit in the general mechanisms of excitation of the nervous tissue.
13 Light adaptation in the cat retina B. SAKMANNand M. FILION. Biophysics. Dept. U.C.L. London, W.C.l. IN AN attempt to localize the site of light adaptation
within the cat retina, a comparison was made of the effect of background light on the late receptor potential and on the ganglion cell response. The increment threshold and the stimulus-response relation were measured for both types of responses in darkness, and at background illuminations of increasing intensity within the scotopic and mesopic range. The increment threshold of the late receptor potential is little affected by raising the background illumination to 7 x 1Om8 1 m/mm,’ whereas the increment threshold of the ganglion cell rises considerably. The intensity range of responses between increment threshold and saturation of the late receptor potential is approximately 4 l0log units of stimulus intensity in darkness. Background light decreases both the intensity range of the response and the maximal amplitude. For the ganglion cells the range of the stimulus-response relation between increment threshold and saturation is approximately 2 ,,Jog units of stimulus intensity at all background illuminations and the amplitude of the maximal response is independent of the background illumination. It is concluded that in the cat retina the site of light adaptation at scotopic and mesopic background illuminations is central to the rod receptors. REFERENCE SAKMANN,B. and CREUTZFELD, J. 0. D. (1969), Arch. ges. Physiol. 313, 168.
14 Dark adaptation in the isolated rat retina W. ERNST and C. M. KEMP. Dept. of Neurophysiology, Institute of Ophthalmology, London,
w.c.1 THE DARK
adaptation of the isolated albino rat retina has been studied, using parallel spectrophotometric and electroretinographic methods. A Ca2+ free perfusing medium containing EDTA was used to isolate the late receptor potential (PIII). After intense lightadaptation, the amplitude of the response (V) of PI11 to a stimulus of constant intensity grows sigmoidally, and continues to change for more than 50 min. at the temperatures used
1198
IUPS-ISCERG Symposium Papers
In contrast, the b-wave (WEINSTEIN, HOBS~Nand DOWLING,1967) and ganglion cell thresholds (WEINSTEINand HOB.SON,1970) stabilize within 10 min. The increase of PI11 ampiitude with time in the later single-exponential phase is the same as the rate of disappearance of metarhodopsin III (465). This correlation has been demonstrated at 24”, 29’ and 34°C. The change in sensitivity for a given bleach is much smaller for PI11 than for the b-wave. Approximately 50 % bleaches do not reduce V,, by as little as 20x, while the light intensity required to produce a given response increases tenfold. REFERENCES WEINSTEIN and HOBSON (1970).Nature, Lord 227, 957. WEINSTEIN, HOBS~Nand DOWLING,J. E (1967). Nature, Lord 215, 134.
15 Afterpotentials
in retinula ceils of the drone’
F. BAUMANNand B&NICE HADJILAZARO. Dept. Physiol. University of Geneva, Switzerland THE RJSTINULA cell of the honeybee drone responds to light by a depolarization of graded amplitude, the receptor potential, which may be followed by either a hyperpoiarizing or a depolarizing afterpotential (HADJILAZARO and BAUMANN,1968). During the hyperpolarizing afterpotential the membrane potential of the cell is greater than the resting or dark potential; during the depolarizing afterpotential it is less. Which of these two afterpotentials dominates the return to dark potential depends on the duration and the intensity of the preceding flash. Thus, the depolarizing afterpotential is most marked after strong stimuli giving rise to a receptor potential of maximum amplitude. The effects on the two afterpotentials of changes in the ionic composition of the bathing medium and of intracellularly applied polarizing currents, as well as measurements of the membrane resistance of the retinula cell, suggest that during the depolarizing afterpotential the membrane is in a state similar to that of the illuminated membrane. It thus appears that the process initiated by the absorption of light by the photopigment and which gives rise to the receptor potential, may continue to be effective for some time after the end of illumination. The hyperpolarizing afterpotential was found to be due, at least partially, to the activity of a pump which after a light flash pumps sodium out and potassium into the retinula cell. REFERENCE HADJILAZARO, B. and BAUMANN, F. (1968). Afterpotentials of the visual cell of the honey-bee drone. Helv. Physiol.Acta 26, CR 351. ’ This work was supported by grants from the Fonds National Suisse de la Recherche Scientifique and the Fondation Sandoz. 18 Damage to pigeon retinae by commercial l&t
sources operating at moderate levels
J. MARSHALL,J. MELLERIOand D. A. PALMER.Institute of Ophthalmology, Judd Street, London, W. C. 1 THE TOXIC action of moderate levels of light upon rat retinae has been reported in the literature. We wished to extend these observations to a retina with more typical rods and cones. We also intended to determine a threshold for damage related to commercial light