CHARACTERISTICS OF SLOW POTENTIALS FROM THE FROG EPIPHYSIS (RANA-ESCULENTA) - POSSIBLE MASS PHOTORECEPTOR POTENTIALS

In situ recorded responses (electropinealogram or EPG) are: (1) not color coded: (2) composed of a fast (lasting < 1sec) photopic component (λmax > 500 nm) and a slower (lasting 1 sec to 1 min) scotopic component (λmax ≈- 500 nm): (3) able to dark-adapt over at least 3.5 log units over a few half hours; (4) dominated by the scotopic (slow) component even at light levels where the spike activity is photopic; (5) show light integration according to Bloch's law up to ≈-5 sec in the dark-adapted state, up to ≈-500 msec in the light-adapted state; (6) also slow in light adapting requiring up to 30 min. The contention that they represent receptor potentials is based on: (a) the lack of a knee in the two-component dark-adaptation curve, (b) the dominance of a scotopic spectral sensitivity curve at photopic adaptation levels and (c) the limited number of cells and cell types in the organ. © 1979.