Dependence of potassium ion and sodium ion exchange on light in the crayfish retina.

The exchange (release resp. uptake) of K+, Rb+, and Na+ ions in the isolated retina of the crayfish Astacus leptodactylus with the surrounding medium was measured using flame photometry and radioisotopic techniques. 1. The net release of K+ into a Na+ and K+ free, choline containing medium, as measured by means of flame photometry, is increased by illumination. 2. The release of 86Rb+, used as an indicator for K+, in retinas preloaded with the radioisotope is also increased during the period of illumination. 3. The net release of Na+ into a Na+ and K+ free medium containing choline, as measured by means of flame photometry, is decreased by illumination. 4. The 22Na+ uptake of the retina is increased by illumination. The increase is greater after an illumination period of 20 min than after one of 2 min. 5. The uptake of 22Na+ of the retina in the dark is increased when the retina has been previously poisoned by ouabain. 6. The results of these experiments are in agreement with the assumption that: a. N ations are the main carrier of the inward current causing the depolarizing receptor potential of Astacus photoreceptor cell membranes and b. the repolarization is caused by a corresponding outflow of K+-ions.