Rapid Effects of Aldosterone in Human Mononuclear Leukocytes*

There is increasing evidence for rapid steroid action on electrolyte transport in human mononuclear leukocytes (HML). In HML, aldoste-rone stimulates the Na+/H+ antiporter within a few minutes. Because a variety of hormones and growth factors activate the Na+/H+ anti-porter via protein kinase C and inositol phospholipids, a possible involvement of inositol-1,4,5-trisphosphate (IP,) in the rapid effects of aldosterone in HML was investigated. The stimulation of IP3 generation was started by the addition of aldosterone, concanavalin A, or other steroids. A significant increase in IP3 levels by aldosterone (1 nmol/L, P < 0.05) was found after 1 min, similar to that found after concanavalin A (25 rg/mL). Aldoste-rone caused a concentration-dependent elevation of IP3 levels, with an apparent ECso of approximately 0.1 nmol/L. Fludrocortisone stimu-lated IPB generation at similar concentrations, whereas a weaker IP