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

Abstract

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 μM) 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.