DEXAMETHASONE-INDUCED SODIUM INFLUX IN HUMAN-LYMPHOCYTES

We evaluated the direct effects of glucocorticoids on intracellular sodium content and cellular transport systems. Cytosolic free sodium concentration ([Na+](i)) was measured in intact human lymphocytes using the sodium-sensitive fluorescent dye sodium-binding benzofuran-isophthalate. Administration of dexamethasone for 60 min increased lymphocytic [Na+](i) from 17.6 +/- 2.0 mmol/L to 24.3 +/- 3.9 nmol/L (n = 12; P < 0.01). The dexamethasone-induced [Na+](i) increase was abolished in the absence of extracellular sodium, by mifepristone and by actinomycin D. The dexamethasone-induced [Na+](i) increase was also seen after inhibition of Na+,K+-ATPase by 1 mmol/L ouabain. The present results indicate that dexamethasone produces a trans-plasma membrane sodium influx probably by early occurring genomic effects.