Two light-induced processes in the photoreceptor cells of Limulus ventral eye.
The dark-adapted current-voltage (I-V) curve of a ventral photoreceptor cell of Limulus, measured by a voltage-clamp technique, has a high slope-resistance region more negative than resting voltage, a lower slope-resistance region between resting voltage and zero, and a negative slope-resistance region more positive than 0 v. With illumination, we find no unique voltage at which there is no light-induced current. At the termination of illumination, the I-V curve changes quickly, then recovers very slowly to a dark-adapted configuration. The voltage-clamp currents during and after illumination can be interpreted to arise from two separate processes. One process (fast) changes quickly with change in illumination, has a reversal potential at +20 mv, and has an I-V curve with positive slope resistance at all voltages. These properties are consistent with a light-induced change in membrane conductance to sodium ions. The other process (slow) changes slowly with changes in illumination, generates light-activated current at +20 mv, and has an I-V curve with a large region of negative slope resistance. The mechanism of this process cannot as yet be identified.
D000818:Animals; D003386:Brachyura; D003623:Dark Adaptation; D004566:Electrodes; D066298:In Vitro Techniques; D008027:Light; D008564:Membrane Potentials / Q000528:radiation effects*; D009799:Ocular Physiological Phenomena; D010786:Photoreceptor Cells / Q000166:cytology / Q000502:physiology* / Q000528:radiation effects; D011830:Radiation Effects