Abstract
Direction selectivity in the ganglion cells is thought to be formed by the combination of cholinergic signals and GABAergic signals. One hypothesis is that the preceding GABAergic inputs to the dendrites of direction selective ganglion cells inhibit the following cholinergic inputs when the direction selective ganglion cells are stimulated from the “null” direction. However, the mechanisms to enable the early arrival of the GABAergic inhibition have not been elucidated. In the present study, we analysed the types of the voltage-gated ionic channels of GFP-positive cholinergic amacrine cells by the patch clamp technique. We found that cholinergic amacrine cells had the specific set of the voltage-gated ionic channels. The cholinergic amacrine cells lacked the voltage-gated Na currents and had very large outward K currents (delayed rectifier and A current). In the previuos reports, it has been reported that GABAergic amacrine cells have the voltage-gated Na currents. Absence of the voltage-gated Na currents can raise a possibility that the speed of signal propagation along dendrites might be different between the cholinergic amacrine cells and the GABAergic amacrine cells. The presynaptic and postsynaptic regulation of cholinergic amacrine cells by the purinergic signaling pathways are also discussed. [Jpn J Physiol 55 Suppl:S49 (2005)]
