Functional Ca 2+ and Na + channels on mouse Schwann cells cultured in serum‐free medium: regulation by a diffusible factor from neurons and by cAMP
Résumé
Abstract Regulation of expression of functional voltage‐gated ion channels for inward currents was studied in Schwann cells in organotypic cultures of dorsal root ganglia from E19 mouse embryos maintained in serum‐free medium. Of the Schwann cells that did not contact axons, 46.5% expressed T‐type Ca 2+ conductances (I CaT ). Two days or more after excision of the ganglia, and consequent disappearance of neurites, I CaT were detectable in only 10.9% of the cells, and the marker 04 disappeared. On Schwann cells deprived of neurons, T‐ (but not L‐) type Ca 2+ conductances were re‐induced by weakly hydrolysable analogues of cAMP, and by forskolin (an activator of adenylyl cyclase) after long‐term treatment (4 days). With CPT cAMP (0.1–2 m m ), 8Br cAMP, db cAMP or forskolin (0.01 or 0.1 m m ), the proportion of cells with I CaT was not significantly different from the proportion in the cultures with neurons. These agents also induced expression in some cells of tetrodotoxin‐resistant Na + currents, which were rarely induced by neurons, but 04 was not re‐induced by cAMP analogue treatments that re‐induced I CaT . Inward currents (Ba 2+ or Na + ) were partly restored ( P < 0.05) on Schwann cells cultured for 6–7 days beneath a filter bearing cultured neurons. In contrast, addition of neuron‐conditioned medium was ineffective. The results suggest that neurons activate, via diffusible and degradable factors, a subset of Schwann cell cAMP pathways leading to expression of I CaT , and activate additional non‐cAMP pathways that lead to expression of 04.