MITOGENIC FACTORS REGULATE ION CHANNELS IN SCHWANN-CELLS CULTURED FROM NEWBORN RAT SCIATIC-NERVE

1. Patch clamp studies were carried out in Schwann cells cultured from newborn rat sciatic nerve to determine the effects of mitogens on vol tage-gated currents without the confounding influences of axonal conta ct and myelin present in vivo. The relevance of the various Schwann ce ll currents to proliferation was assessed using assays of [H-3]thymidi ne incorporation. 2. Treatment of cultured Schwann cells with known mi togens, namely axon fragments (AF), myelin fragments (MF), or glial gr owth factor in combination with forskolin (GGF+F), increased the magni tudes of delayed rectifying potassium (K+) and sodium (Na+) currents. 3. In both control and mitogen-treated cells, the magnitude of net out ward current paralleled clearly the magnitude of the cells' proliferat ive response. 4. The K+ channel-blocking quaternary ammonium ions, tet rabutylammonium (TBuA), tetrapentylammonium (TPeA) and tetrahexylammon ium (THeA), but not the Na+ channel blocker tetrodotoxin (TTX), reduce d proliferation in a dose-dependent fashion offering further evidence for a role for K+ channels in Schwann cell proliferation. 5. Voltage-g ated chloride (CI-) currents were observed in both control and mitogen -treated cells. Addition of the Cl- channel blockers, -acetamido-4'-is ocyanatostilbene-2,2'-disulphonate (SITS) or 4,4'-diisothiocyanatostil bene-2,2'-disulphonate (DIDS), to the culture media enhanced prolifera tion. 6. The possible intermediary role of the Schwann cell resting po tential was explored in ion substitution experiments by increasing the K+ concentration of the media and by adding ouabain. Both manipulatio ns inhibited Schwann cell mitosis. 7. Comparison of the expression of functional ion channels in vitro with that previously described for Sc hwann cells in vivo suggests a difference in the Schwann cell response to the membrane fragment mitogens and their intact counterparts in re gard to the regulation of ion channels. MF up-regulates the number of functional channels, whereas the elaboration of myelin (or a factor re lated to its presence) in vivo appears to down-regulate channel expres sion, at the cell soma of myelinating Schwann cells. In addition, axon al contact may be required for normal expression of functional inwardl y rectifying K+ channels.