Über die Ionen-Abhängigkeit des Rezeptorpotentials der Retina von Astacus leptodactylus / The Ion-dependence of the Receptor Potential of the Visual Cell of the Crayfish

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Abstract
The mass response of the photoreceptor cells of the isolated crayfish-retina (Astacus leptodactylus) (receptor potential ReP) resulting from short and long light stimuli, has been measured with external electrodes. The ionic composition of the saline by which the preparation was perfused was changed and the influence of those changes on the ReP was measured under constant stimulus conditions. When all sodium ions are substituted by potassium ions, the height of the ReP is reversibly both decreased and shortened (Figs. 3 and 4). When all sodium ions are almost substituted by choline ions, (the remaining sodium concentration at the photoreceptor cells being less than 1 mMol/Z) the sensitivity to light adaptation is drastically and reversibly increased. Mainly due to light adaptation the ReP becomes smaller and shorter whereas the latency period increases (Figs. 5 - 8). If the concentration of extracellular calcium is reduced to less than 0.1 mMol/l, the decrease of the REP is considerably and reversibly slowed down while the increase of the REP remains almost unchanged (Fig. 9). If magnesium ions are also lacking the effect is even more pronounced (Figs. 10 and 11). All these changes of the ReP are probably due to actions of the ions on the membrane of the photoreceptor cells or its immediate vicinity. The results do not allow an unequivocal decision whether the ReP is due to an increased conductance (CIM) of the photoreceptor cell membrane or due to a change in the action of an electrogenic ion pump (EPM). But considering the results as a whole, and especially those from the low Ca- and low Mg-experiments, it seems unlikely that the ReP is caused by an EPM.

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