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Insulin, C-peptide, and proinsulin are released by insulinoma cells in response to arterial calcium stimulation, whereas CgA and NSE are not released. Also from our study it seems that PP may be released by healthy islet cells after calcium stimulation.

The effects of the extracellular potassium concentration on the expression of four steroidogenic cytochromes P-450 (CYP11B2, CYP11B1, CYP11A1, and CYP21A1) in cultured rat adrenal zona glomerulosa cells were studied by Northern blot analysis. At a potassium concentration of 6.4 mM, the CYP11B2 messenger RNA (mRNA) level and aldosterone production were undetectable. Upon increasing the potassium concentration to 18 mM, CYP11B2 mRNA and aldosterone production became measurable and reached a plateau within 4 days. The high potassium concentration also caused distinct increases in the levels of CYP11B1, CYP11A1, and CYP21A1 mRNA, comparable to those induced by ACTH. ACTH did not affect the CYP11B2 mRNA level at the lower potassium concentration. In zona fasciculata cells, CYP11B2 expression was not inducible by potassium; CYP11B1, CYP11A1, and CYP21A1 mRNA levels increased in response to ACTH, but not in response to a high potassium concentration. According to these results, 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 steroidogenic enzymes.

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