Photoreceptor responses to light in the isolated pineal organ of the trout, Salmo gairdneri

Photoreceptor potentials were recorded intracellularly from the isolated pineal organ of the teleost, Salmo gairdneri, maintained in tissue culture medium for 2-20 h. After electrophysiological characterization the photoreceptor cells were iontophoretically injected with Lucifer Yellow or with horseradish peroxidase for subsequent morphological identification. A brief flash of light elicited a hyperpolarization which was graded with light intensity in the dark-adapted photoreceptor. For dim flashes, the responses were purely monophasic. At higher intensities responses either remained purely monophasic or displayed an initial transient wave which became prominent for supersaturating intensities. The latency of the responses and their rise time decreased with increasing light intensity. Threshold responses showed latencies of about 600 ms, reached a maximum in about 1100 ms and returned to the dark potential in about 5 s. Saturating flashes considerably diminished the latency to 55 ms, the rise time to about 250 ms, but increased the time of recovery from peak to dark potential up to 60 s. Intracellular responses to background illumination exhibited two different response types. One type repolarized immediately, when the background light was extinguished, whereas the other type was characterized by a slow recovery of the dark potential. The spectral sensitivity of all intracellular recorded photoreceptors peaked at lambda max = 520-530 nm.