Regulation of mineralocorticoid biosynthesis by calcium and the StAR protein

In adrenal zona glomerulosa cells, the calcium messenger system is the majo r signaling mechanism activated by physiological stimulators of aldosterone production. We present here evidence for a dual site of action of the calc ium signal: 1) Calcium influx into the mitochondrion is a prerequisite to t he activation of steroidogenesis. This calcium entry leads to a rise in mit ochondrial calcium concentration and to an increase in intramitochondrial c holesterol transfer and Steroidogenic Acute Regulatory (StAR) protein accum ulation in inner mitochondrial membranes. 2) Calcium also exerts a genomic regulatory effect by activating transcription of the StAR gene.