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.