The Significance of Metabolic Energy and the Ion Pump for the Receptor Potential of the Crayfish Photoreceptor Cell

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Abstract
Isolated crayfish retinas were poisoned by dinitrophenol (DNP) or ouabain (OU). The changes of the extracellularly recorded receptor potential (ReP) evoked by short or long stimuli were measured. The changes of the shape of the ReP after poisoning by OU are the same, except the transient increase, as appear after depolarizing the retina by high external potassium concentration. DNP has different effects on the ReP. It causes a prolongation of the amplitude hmax and an increase of the shape quotient hmax/he (Fig. 9). Expecially the rate of decrease of the excitability under different stimulus programs was measured (Tab. 5). DNP experiments show that the inexcitability occurs the earlier the higher the incident light intensity is. The time needed depends on the stimulating efficiency of the light rather than on the direct amount of energy. The loss of excitability rather depends on the energy of the total light applied than on the stimulus pattern. Concerning the inexcitability OU shows the same effect as DNP: it occurs the earlier the more the retina is excited. These results contradict the hypothesis that the receptor potential is a consequence of a light induced change of the activity of an electrogenic pump mechanism. Fig. 10 shows the electrogenic pump mechanism (EPM) as opposed to the conductance increase mechanism (CIM).

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