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H Suominen, S Nymark, K Donner, A Koskelainen; Temperature Effects On Frog Cone Sensitivity . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1420.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Spontaneous thermal activations of the visual pigment constitute an intrinsic background of light-like activity ("dark light") in photoreceptor cells. The rate of thermal activation of long-wavelength-sensitive cone pigments (L-cone pigments) could be high enough to "light-adapt" the cell. Our purpose is to test the hypothesis that thermal pigment activation determines dark-adapted sensitivity in L-cones. Thermal activation rates will increase with warming, whereby according to the hypothesis (1) dark-adapted sensitivity should decrease and (2) higher intensities of adapting background light should be required to achieve adaptational changes in cone sensitivity. Methods: Aspartate-isolated mass responses of 562-nm cones were recorded by ERG from isolated frog retinas in the temperature range 3-25 ºC. The cone response was obtained by subtracting photoresponses to 552 nm flashes from responses to rod-equivalent 642 nm flashes. Fractional sensitivities (defined by the half-saturating flash intensity) were determined in darkness and at several intensities of steady background illumination (621 nm). Results: Above ca. 10 ºC, log fractional sensitivity decreased linearly with rising temperature. Below 10 ºC, sensitivity was independent of temperature. Strong background light (ca. 2000 Rh*/s) made sensitivity temperature-independent over the whole temperature range studied. The intensity of steady background light required to depress cone sensitivity by half increased monotonically with warming in the range 10-25 oC, from ca. 20 Rh*/s to 1000 Rh*/s. Conclusion: The results are in qualitative agreement with the predictions. However, even when corrected for the temperature-dependence of integration time, the measured differences over the range 10-25 ºC appear too large to be explained simply by changes in the rate of thermal pigment activations.
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