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S. Nymark, H. Heikkinen, K. Donner, A. Koskelainen; Temperature Resembles Background Light in Its Effects on Fractional Photoresponses of Frog L-Cones. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5821.
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Exposing photoreceptors to steady background light makes photoresponses faster and decreases the fraction of the maximal response amplitude elicited per photoisomerization. This is mainly due to faster response recovery. Raising temperature also accelerates photoresponses and decreases fractional sensitivity. In rods the whole response accelerates while retaining its shape (Baylor et al. 1984; Lamb 1983; Nymark et al. 2005). In this work we wanted to test whether the change in the responses of amphibian long-wavelength-sensitive cones (L-cones) is similar to that observed in rods regardless of the differences in e.g. cell morphology and pigment stability.
Aspartate-isolated cone responses to brief flashes of 642 nm light were recorded by electroretinogram (ERG) technique across isolated frog (Rana temporaria) retinas. The response of the L-cones was isolated by a subtraction procedure designed to remove the rod response. The fractional photoresponse was studied at different temperatures in the temperature range 7-25°C.
Temperature did not affect the activation and revovery phases of photoresponses equally. Although a modest change in the activation phase of fractional photoresponses was evident, responses mainly seemed to peel off from a common rising edge at earlier times the higher the temperature. This is a classic hallmark of light adaptation with increasing steady background light.
The activation phase of fractional photoresponses is remarkably temperature-invariant in frog L-cones, while the recovery phase shows much stronger changes similar to those seen under adaptation to different background light intensities.
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