Voltage-gated currents of putative GABAergic amacrine cells in primary cultures and in retinal slice preparations.

To analyze the voltage-dependent ionic conductances of putative GABAergic amacrine cells developing in vitro, whole cell patch clamp recordings were carried out on identified neurons in monolayer cultures from embryonic chick retinae. These recordings were directly compared with those performed on amacrine cells in chick retinal slice preparations. Current responses to depolarizing voltage steps observed in cultured neurons could be separated into at least four different components. A small tetrodotoxin-sensitive sodium inward current was observed in approximately 50% of the cells. The considerably larger outward potassium current consisted of a transient 4-aminopyridine-sensitive component and a sustained component. The latter was reduced in the presence of both tetraethylammonium chloride and Co2+ and thus was probably composed of two conductances. In addition, a Ca(2+)-carried inward current of small amplitude could be identified. Voltage-sensitive currents measured in amacrine cells of retinal slices were very similar. Again, only about half of the cells exhibited sodium currents. Potassium currents contained the above components, but their contributions to the whole cell current seemed to be different. Together with previous findings these results suggest that immature retinal neurons in dissociated cultures undergo a differentiation process similar to that occurring in vivo.