Membrane resistance properties of pineal photoreceptors in the trout.

Intracellular recordings were obtained from pineal photoreceptors of the trout Salmo irideus. Illumination produced graded hyperpolarizing responses whose time course resembled that of retinal cones in lower vertebrates. Current-voltage relations were derived by using a voltage-clamp technique in the dark and during illumination. Membrane resistance values obtained in the dark were about 550 M omega, and they increased during illumination. The extrapolated reversal potential of the photocurrent is about 55 mV above the dark membrane potential, indicating that an ionic mechanism similar to that in retinal photoreceptors may be involved.