Measurement of a steady state current in the dark in photoreceptors of the barnacle.

Receptor potentials are measured extracellularly by means of an air gap method along the optic nerve of the median and the lateral photoreceptor of the barnacle. Both photoreceptors have an outward dark current (photoreceptor positive with respect to the nerve) which is diminished ap­ proximately 70% during the plateau phase of the receptor potential. Ouabain abolishes dark current and receptor potential in the sam e proportion. W ith a Lim ulus lateral eye preparation a dark cur­ rent and light induced current changes were measured which had the same polarity and a similar magnitude as the receptor currents of the barnacle.