EFFECT OF DEXAMETHASONE ON VOLTAGE-GATED CA2+ CHANNELS AND CYTOSOLIC CA2+ IN RAT CHROMAFFIN CELLS

THE present study examined whether the synthetic glucocorticoid dexame thasone (DEX) can modulate voltage-gated Ca2+ channel (VGCC) activity, and as consequence agonist-induced increases in cytosolic Ca2+ in cul tured rat adrenal medullary chromaffin (RAMC) cells. Exposure to 1 mu M DEX for 48 h significantly increased peak VGCC current (Delta +140%) . DEX treatment also significantly potentiated the increases in cytoso lic Ca2+ in response to submaximal stimulatory concentrations of KCl ( Delta +64%) and nicotine (Delta +32%). The Ca2+ channel agonist BAY K- 8644 increased both VGCC current (Delta +109%) and potentiated the KCl -stimulated increase in cytosolic Ca2+ (Delta +35%) to a comparable ex tent to that seen with DEX. These data suggest that DEX treatment incr eases VGCC activity, and that this increased Ca2+ influx leads to pote ntiation of agonist-induced increases in cytosolic Ca in RAMC cells.