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. 1972 Dec;227(3):815–838. doi: 10.1113/jphysiol.1972.sp010060

Light-induced changes in the electrical impedance of the isolated frog retina

J A Coles
PMCID: PMC1331288  PMID: 4539862

Abstract

1. An isolated frog retina was mounted in an impedance chamber and superfused on its vitread surface.

2. Changes in the real part of the impedance (ΔR) and also in the imaginary part were measured using alternating current in the frequency range 1-300 kHz passed from one surface of the retina to the other.

3. Under most conditions, the response to a flash of light, measured at frequencies below about 100 kHz, was a decrease in the real part of the impedance (ΔR < 0).

4. The geometry of the electrodes was such that the system was particularly sensitive to changes in the impedance of the layer of photo-receptor outer segments. It was confirmed that most of ΔR did arise here and that it was mediated by the absorption of light in rod photo-pigment.

5. The magnitude of ΔR increased when the channels between the outer segments were constricted, e.g. by osmotic swelling of the outer segments. In addition to this increase, a further increase was seen following the commencement of recording in most of the experiments from which usable measurements were obtained.

6. In such retinas, the magnitude of ΔR was greatest when measured at a frequency in the range 3-32 kHz, the largest changes being of the order of 0·1% of the resting value. A light flash bleaching about 1% of the pigment was sufficient to produce this. The onset of ΔR was apparent within 1 msec of the flash (at 15° C); it reached a maximum in 0·5-4 sec and then returned towards the base line.

7. The main component of ΔR was attributed to a decrease in the resistance of the spaces between the outer segments. In addition, there was a resistance increase which occurred at some other site, probably the surface membrane. The first of these components had an onset slightly more rapid than the second, and both occurred irrespective of whether the major cation in the superfusate was sodium or potassium.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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