Cone and possible rod components of the fast photovoltage in the frog eye: a new method of measuring cone regeneration rates in vivo.

ELECTIUCAL potentials produced by the eye or excised retina in the first few msec after an intense flash of light were discovered by BROWN and M~K~I (1964). The “Early Receptor Potential” or the Fast Photovol~~ (FPV), as this response has been called by HAGINS and MCGAUGHY (1967), has been shown to be very probably produced by a molecular change in the rhodopsin or pigment molecules. Recent papers by CONE (1967) and PAK and Boas (1967) present evidence of the apparent molecular nature of the FPV and give references to earlier work. Early work included studies of rod and cone components of the FPV in all-rod animals (albino rats) and all-cone animals (Mexican ground squirrel) (CONE, 1964; PAK and EBREY, 1966), but not in an animal with both rods and cones. It therefore appeared interesting to study the FPV from a mixed rod-and-cone eye, to see if these components could be separated in the same eye. Frogs (Runa pipiens) were studied since they have been shown to contain at least three receptors, cones (A, near 560 nm), pink rods {containing rhodopsin) and green rods (blue absorbing) (GRANIT, 1941; DIUZTNALL, 1967; DINNER and Rusm~, 1959; NILSSON, 1964). It seemed that it might be possible to separate rod and cone components of the FPV by comparing the FPV action spectrum in the dark-adapted state, after at least 12 hr in the dark, and in the light-adapted state, after exposure to a continuous white light or a sequence of bright blue light flashes. Different rates of recovery after a bright bleaching light can also be used to separate rod and cone ~rn~nen~, since it is known that frog rods take over an hour to regenerate (I&wr, 1939), while cones (in humans) recover in a few minutes (RUSHT~N, 1963; WBALE, 1959). Since this study was started, B. GOLDS= (1967, 1968) has published work on the FPV of an excised frog retina, He concludes that the FPV is predominately from the cones. He was also able to separate an apparent rod component and reports a recovery of the FPV in the excised retina comsi&~bly slower than reported here in viva. The action spectra reported here do not agree with his at wavelengths below about 520 run. These differences will be discussed later.