POTASSIUM INDUCES MULTIPLE STEROIDOGENIC ENZYMES IN CULTURED RAT ZONAGLOMERULOSA CELLS

The effects of the extracellular potassium concentration on the expres sion of four steroidogenic cytochromes P-450 (CYP11B2, CYP11B1, CYP11A 1, and CYPB1A1) in cultured rat adrenal zona glomerulosa cells were st udied by Northern blot analysis. At a potassium concentration of 6.4 m M, the CYP11B2 messenger RNA (mRNA) level and aldosterone production w ere undetectable. Upon increasing the potassium concentration to 18 mM , CYP11B2 mRNA and aldosterone production became measurable and reache d a plateau within 4 days. The high potassium concentration also cause d distinct increases in the levels of CYP11B1, CYP11A1, and CYP21A1 mR NA, comparable to those induced by ACTH. ACTH did not affect the CYP11 B2 mRNA level at the lower potassium concentration. In zone fasciculat a cells, CYP11B2 expression was not inducible by potassium; CYP11B1, C YP11A1, and CYP21A1 mRNA levels increased in response to ACTH,but not in response to a high potassium concentration. According to these resu lts, potassium initiates CYP11B2 biosynthesis most likely at the level of transcription or by increasing mRNA stability. Potassium also has a zona glomerulosa-specific inductive effect on three other steroidoge nic enzymes.