Effect of ions on the light-sensitive current in retinal rods

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Abstract
The effect of ions on the light-sensitive current of retinal rods was studied by sucking the inner segment into a tightly fitting capillary with the outer segment projecting into a flowing solution. This new method showed that the light-sensitive pathway, in which Na+ is the normal carrier of current, has an ionic selectivity different from that of other known Na+ channels. External Ca2+ has a striking effect on the current, which increased about 20-fold when all Ca2+ was removed. Reducing the Na+ concentration gradient greatly prolonged the response to a flash of light, as would be expected if internal Ca2+ blocks Na+ channels and if light releases Ca2+ which is subsequently extruded by a Na+-Ca2+ exchange mechanism.