The respiration of the isolated rod outer limb of the frog retina

The respiration of the isolated frog rod outer limb has been measured in the Cartesian diver. The outer limbs respire in Ringer solution without the addition of substrates, but the rate of respiration is increased by the addition of fructose diphosphate or succinate. The respiration is cyanide-sensitive, and therefore presumably mediated by the cytochromes. The Q(OO2) in 0.01 M fructose diphosphate is -1.0 microl. oxygen per mg. dry weight per hour at 20 degrees C. This is lower than the Q(OO2) of whole frog retina, but comparable with it and many other tissues. The respiratory rate is independent of the state of dark adaptation (rhodopsin content) of the outer limbs. The metabolism of the outer limb is probably adequate to provide the DPN required for the maintenance of the rhodopsin concentration necessary for vision.