Functional Ca²⁺ and Na⁺ channels on mouse Schwann cells cultured in serum‐free medium: regulation by a diffusible factor from neurons and by cAMP

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 Ca2+ conductances (ICaT). Two days or more after excision of the ganglia, and consequent disappearance of neurites, ICaT 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 Ca2+ 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 mM), 8Br cAMP, db cAMP or forskolin (0.01 or 0.1 mM), the proportion of cells with ICaT 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 ICaT. Inward currents (Ba2+ 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 IcaT, and activate additional non-cAMP pathways that lead to expression of 04.

Exposure to cAMP and β‐adrenergic stimulation recruits CaV3 T‐type channels in rat chromaffin cells through Epac cAMP‐receptor proteins

“…The partial antagonistic action of H89 above 0.3 μ m could be due to unspecific effects of the PKA inhibitor that at higher concentrations may inhibit various kinases (Davies et al 2000). Our data are in good agreement with previous reports showing that a cAMP‐dependent pathway is involved in the recruitment of T‐type channels in Schwann and neuroendocrine cells (Beaudu‐Lange et al 1998; Mariot et al 2002), although both reports do not mention the existence of PKA‐dependent or PKA‐independent pathways. A PKA‐independent down‐regulation of the α6 subunit of GABA A receptors in mature rat cerebellar granule cells has also been shown (Thompson et al 2000).…”

“…Cells were plated on plastic dishes pretreated with poly‐ l ‐ornithine (1 mg ml −1 ) and laminin (5 μg ml −1 in L‐15 carbonate), incubated at 37°C in a water‐saturated atmosphere with 5% CO 2 and used within 2–6 days of plating. The culture medium was made serum‐free to prevent different batches from inducing different effects on the recruitment of T‐type channels (see Beaudu‐Lange et al 1998). The medium contained: Dulbecco's modified Eagle's medium (DMEM), penicillin–streptomycin 0.5% and gentamycin 0.25%, and was not changed during the culture period.…”

“…Various reports indicate that cAMP‐dependent pathways are critical elements for recruiting GABA A receptors (Thompson et al 2000) and voltage‐gated Na + and Ca 2+ channels (Yuhi et al 1996; Beaudu‐Lange et al 1998; Doležal et al 2001; Mariot et al 2002) in neurones, glial and neuroendocrine cells. In the case of chromaffin cells, several reports suggest that the basal levels of cAMP are low but can rise following adenylate cyclase activation, phosphodiesterase inhibition or β‐adrenoceptor (β‐AR) stimulation (Parramón et al 1995; Carabelli et al 2001; Carbone et al 2001).…”

ATP stimulation of P2X7 receptors activates three different ionic conductances on cultured mouse Schwann cells

“…Schwann cells were cultured from excised dorsal root ganglia from OF1 mouse embryos (E19) as previously described (Amédée et al ., 1991; Beaudu‐Lange et al ., 1998). Mice were killed by decapitation.…”

Expression of Nav1.6 sodium channels by Schwann cells at neuromuscular junctions: Role in the motor endplate disease phenotype

“…Boudier, unpublished results) that could be accounted for by an increase in the number of Schwann cells and the extension of Schwann cell processes (Lubischer and Thompson, 1999). Previous studies have already reported the presence of tetrodotoxin‐sensitive sodium currents in Schwann cell cultures derived from rabbit, rat, and frog sciatic nerves (Shrager et al, 1985; Miyazaki et al, 1994), or from mouse dorsal root ganglia (Beaudu‐Lange et al, 1998). Using excised patches, Chiu (1993) recorded sodium currents in freshly isolated Schwann cells from 10‐week‐old rabbit sciatic nerve.…”