Temperature-dependence of rod photoresponses from the aspartate-treated retina of the frog (Rana temporaria)

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Abstract
The effects of temperature changes on rod photoresponses were studied by recording the aspartate-isolated mass receptor potential in the dark-adapted retina of the frog Rana temporaria. The amplitude of saturating responses, indicating the magnitude of the dark current, increased linearly with temperature in the measured range 6-26 degrees C, extrapolating to zero dark current at 0 degrees C. Sensitivity was maximal around 18 degrees C but the decrease towards lower temperatures was shallow. The results show that rod phototransduction in the frog Rana temporaria is adapted to lower temperatures than in the tropical toad Bufo marinus. Responses to dim flashes were, approximately up to peak, well fitted by the same 'independent activation' model with four delay stages as have been found to best describe current responses from single toad rods. The kinetics (reciprocal time-to-peak) showed Arrhenius-type temperature-dependence with apparent activation energy 12.4 kcal mol-1 and Q10 = 2.1.