SODIUM DEPENDENCY OF THE INWARD POTASSIUM RECTIFIER IN HORIZONTAL CELLS ISOLATED FROM THE WHITE BASS RETINA

The ionic properties underlying the inwardly rectifying potassium curr ent in cultured voltage-clamped white bass horizontal cells were studi ed. Anomalous rectification was apparent upon membrane hyperpolarizati on with a reversal potential depolarized from the predicted value of E (k). In raised extracellular potassium, the current increased and the reversal potential shifted toward a more depolarized membrane potentia l. Solutions containing decreased sodium caused a rapid decrease in th e inward rectifier current but only slightly affected the reversal pot ential. Extracellular cesium or barium caused a reversible voltage-dep endent reduction of the inward current. We interpret these results to mean that the inward rectifying channel in white bass horizontal cells is mainly permeable to potassium ions, but is sodium dependent. It ma y shape the photoresponses of the horizontal cells and may contribute to a hyperpolarization activated conductance increase measured in situ .