A Photon Counting Microspectrophotometer for the Study of Single Vertebrate Photoreceptor Cells

Abstract

In order to have a satisfactory description of how the visual system works, particularly a description on which one can base adequate quantitative as well as qualitative theories of visual function, including both normal and abnormal color perception, it’s obviously necessary to understand how photoreceptor cells transduce light signals. This paper concerns two techniques that may be useful in improving our knowledge in this area. The first is an improved microspectrophotometer for studying the pigments in single receptors. The second is a microchemical technique for the measurement of light induced reactions in single receptor outer segments. To begin with I would like to go briefly into some of the history of single receptor microspectrophotometry. Until reasonably accurate measurements on single cones in the goldfish were reported by MARKS and myself (1), MARKS (2, 3), and confirmed by LIEBMAN and ENTINE (4), and in human and rhesus monkey receptors by MARKS, DOBELLE and MACNICHOL, (5), and by BROWN and WALD (6), there was no direct evidence that there are three kinds of cones each having a different pigment in organisms known to have trichromatic vision, although much indirect evidence has accumulated over the course of many years from psychophysical and behavioral measurements, the study of defective color perception, and more recently, retinal densitometry. However, for a variety of reasons, the promising work on primate cones of the early 1960’s was soon dropped in the two laboratories in which it was done. Although LIEBMAN has reported confirmatory work, neither he nor anyone else to my knowledge has published any more data on single primate cones since then.