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Temperature effects on spectral properties of red and green rods in toad retina

Published online by Cambridge University Press:  30 January 2003

PETRI ALA-LAURILA ,
PIA SAARINEN ,
RAULI ALBERT ,
ARI KOSKELAINEN  and
KRISTIAN DONNER
PETRI ALA-LAURILA
Affiliation:
Laboratory of Biomedical Engineering, Helsinki University of Technology, FIN-02015 HUT, Finland
PIA SAARINEN
Affiliation:
Department of Biosciences, Division of Animal Physiology, FIN-00014 University of Helsinki, Finland
RAULI ALBERT
Affiliation:
Laboratory of Biomedical Engineering, Helsinki University of Technology, FIN-02015 HUT, Finland
ARI KOSKELAINEN
Affiliation:
Laboratory of Biomedical Engineering, Helsinki University of Technology, FIN-02015 HUT, Finland
KRISTIAN DONNER
Affiliation:
Department of Biosciences, Division of Animal Physiology, FIN-00014 University of Helsinki, Finland
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Abstract

Temperature effects on spectral properties of the two types of rod photoreceptors in toad retina, “red” and “green” rods, were studied in the range 0–38°C. Absorbance spectra of the visual pigments were recorded by single-cell microspectrophotometry (MSP) and spectral sensitivities of red rods were measured by electroretinogram (ERG) recording across the isolated retina. The red-rod visual pigment is a usual rhodopsin (λmax = 503.6 nm and 502.3 nm at room temperature (21°C) in, respectively, Bufo marinus and Bufo bufo), that of green rods (λmax = 432.6 nm in Bufo marinus) belongs to the “blue” cone pigment family. In red rods, λmax depended inversely and monotonically on temperature, shifting by −2.3 nm when temperature was raised from 0°C to 38°C. Green-rod λmax showed no measurable dependence on temperature. In red rods, warming caused a relative increase of sensitivity in the long-wavelength range. This effect can be used for estimating the energy needed for photoexcitation, giving Ea = 44.3 ± 0.6 kcal/mol for Bufo marinus rhodopsin and 48.8 ± 0.5 kcal/mol for Bufo bufo rhodopsin. The values are significantly different (P < 0.001), although the two rhodopsins have very similar absorption spectra and thermal isomerization rates. Our recording techniques did not allow measurement of the corresponding effect at long wavelengths in green rods. Although spectral effects of temperature changes in the physiological range are small and of little significance for visual function, they reveal information about the energy states and different spectral tuning mechanisms of the visual pigments.

Keywords

RhodopsinSpectral sensitivityAbsorbanceTemperature effectsActivation energy
Type
Research Article
Information
Visual Neuroscience , Volume 19 , Issue 6 , November 2002 , pp. 781 - 792
Copyright
2002 Cambridge University Press

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