Downregulation of voltage-gated sodium channels by dexamethasone in clonal rat pituitary cells

The effect of chronic dexamethasone (DEX) treatment (4-5 days) on Na+ channel expression was examined in a clonal strain of rat pituitary cells secreting growth hormone (GH) and prolactin (GH3 cells). Using whole-cell patch clamp recording, we found that DEX (1 muM) induces an 80% decrease in Na+ current density. No concomitant changes in current kinetics or voltage dependence of Na+ channel function were detected. Instead, the decrease in current density was accompanied by a similar reduction in maximal Na+ conductance, suggesting the loss of Na+ channels from the plasma membrane. Accordingly, saxitoxin binding assays carried out on intact cells showed that the average number of Na+ channels per cell is markedly decreased by DEX Thus, this glucocorticoid inhibits the cell surface expression of Na+ channels when chronically applied to GH3 cells. (C) 2003 Elsevier Science Ireland Ltd. All rights reserved.