Generation of b-wave currents in the skate retina.

Potassium kinetics within the skate retina were monitored extracellularly with K+-selective electrodes. Two sources of K+ efflux were detected in response to photic stimulation: one in the distal retina in the region of the outer plexiform layer, and the other at a more proximal location near the border between the inner nuclear and inner plexiform layers. The magnitude of the K+ efflux at these retinal depths was affected differently by spot and full-field illumination, suggesting that the two sources originate from different classes of neuron. There is evidence that both sources are associated with current sinks provided by the Müller cells, thereby establishing radial current paths along the lengths of these elements. We have proposed a model in which asymmetries in the magnitudes of these currents give rise to the b-wave of the electroretinogram. Extracellular field potentials recorded differentially at various retinal depths, and in response to changes in stimulus configuration, were consistent with predictions of the model.