Voltage gradients across the receptor layer of the isolated rat retina

Abstract

The electroretinogram (ERG) of the isolated rat retina was investigated by recording potential differences developed between 2 micropipettes. In the uniformly illuminated receptor layer, voltage gradients at 90.degree. to the long axes of the receptors were negligible in comparison with the radial voltage gradients. When all transsynaptic neural activity was abolished, the photoresponse recorded across the receptor layer was very different from the photoresponse recorded across the inner retinal layer. The photoresponse developed across the inner retinal layers, slow P III, developed slowly and the peak voltage was approximately proportional to log flash energy. The photovoltage across the receptor layer rose rapidly to its peak, before a significant fraction of slow P III developed. The faster photovoltage (receptor potential) increased with flash intensity according to the hyperbolic function characteristic of photoreceptors. The faster photovoltage could be split into 2 components. Between the tips of the outer limbs and the bases of the inner limbs, it had a simple wave form. In the region between the bases of the inner limbs and the receptor synapses, there was an additional peak (nose) to the photovoltage. In the scleral portion of the receptor layer, the photovoltage approximately equaled the dark voltage. In the remaining, vitreal portion of the receptor layer the photovoltage exceeded the dark voltage. Photocurrent divergence was measured, and the source of photocurrent extended further vitreally than the base of the outer limb. The photoresponse generated in the outer limbs is apparently modified by an active process which occurs in portions of the rods which are nearer the synapse.