Development of membrane currents in mammalian neuroventricular cells from the early neural tube stage in vitro: aspects of the neuronal lineage.

Neuroepithelial cells from the murine brain anlage at the early neural tube stage (embryonic day 9 1/2, stage 15) were cultured. Their morphology and the development of membrane currents were studied during 2 weeks in culture. Immediately after dissociation the cells were equal in shape and no morphological or ultrastructural differences were evident. Patch-clamp measurements within the first 2 h, however, showed different membrane properties. Either sodium inward currents or potassium outward currents were observed in these undifferentiated cells, but no combined inward and outward currents were found. This would mean that some of the neuroventricular cells, but obviously not all of them, display neuronal membrane properties (sodium currents) in the immediate post neural plate stage. After 1 day, developing neurons could be identified morphologically by neurotubuli and process formation. The transformation of these cells into neurons was electrophysiologically characterized by an increasing sodium channel density and the expression of various kinds of potassium channels. After 4 days the vast majority of the neurons was electrically excitable, i.e. they could generate action potentials. The standard electrical profile at this time was characterized by a sodium inward current followed by a delayed potassium outward current. In the following days the complexity of membrane currents increased in some neurons by the emergence of transient potassium currents. After 2 weeks in culture different neuronal phenotypes could be identified.