Nongenomic effects of aldosterone on Ca2+ in M-1 cortical collecting duct cells

Abstract

Background. Aldosterone at physiological levels induces rapid (<5 min) increases in intracellular protein kinase C (PKC) activity and a rise in calcium and pH in mineralocorticoid hormone target epithelia, such as distal colon and sweat gland. The end targets of these rapid responses in epithelia are Na+/H+ exchange and K+ channels. Methods. The mouse cortical collecting duct (CCD) M-1 cell line was grown to confluency and loaded with Fura-2 for spectrofluorescence measurements of intracellular free calcium at 37°C bathed in Krebs solution. Results. Aldosterone (1 nmol/L) produced a rapid, transient peak increase in [Ca2+](i) in M-1 cells. This effect was abolished upon removal of extracellular Ca2+, but was unaffected by pretreatment with spironolactone (10 μmol/L) or actinomycin D (10 μmol/L). However, pretreatment with the specific PKC inhibitor chelerythrine chloride (1 μmol/L) prevented the aldosterone-induced rise in [Ca2+](i). Dexamethasone, at a concentration 10, 000-fold higher than aldosterone (10 μmol/L), also produced a transient increase in [Ca2+](i), but this response was significantly smaller than that of aldosterone. In contrast, hydrocortisone had no effect on [Ca2+](i) at either nmol/L or μmol/L concentrations. Both of the sex steroids, 17β-estradiol (10 nmol/L) and progesterone (10 nmol/L), induced protein kinase C-dependent increases in [Ca2+](i). Conclusions. Aldosterone and sex steroid hormones activate intracellular calcium signaling in CCD cells via a nongenomic PKC-dependent pathway, which may have important implications for renal transport.