Evidence that angiotensin II decreases mitochondrial calcium in the glomerulosa cell

Abstract

The present studies were performed using primary monolayer cultures of bovine glomerulosa cells to determine whether the elevation in cytosolic calcium concentration produced by angiotensin II was accompanied by an elevation in mitochondrial calcium. Exchangeable mitochondria calcium content was assessed indirectly by measuring the changes in cytosolic calcium concentration and calcium efflux produced by the mitochondrial uncoupler, carbonyl cyanide m-chlorophenylhydrazone (CCCP). Total mitochondrial calcium content was also assessed directly by atomic absorption spectroscopy. CCCP had a direct effect to promote calcium release from an oligomycin/antimycin-sensitive (mitochondrial) calcium pool in permeabilized cells. In intact cells, CCCP caused rapid reductions in cellular ATP content and the ratio of ATP to ADP. Still, its effects on calcium dynamics were exerted primarily at the mitochondrial level as evidenced by inhibition with ruthenium red, but not dantrolene. As expected, angiotensin II produced a rapid increase in calcium efflux and an equally rapid and sustained increase in cytosolic calcium concentration. Nonetheless, CCCP-stimulated elevations in cytosolic calcium concentration and calcium efflux were reduced by angiotensin II in a concentration-dependent manner. Total mitochondrial calcium content was also lower in angiotensin-treated than in control cells. These results indicate that angiotensin II causes a net decrease in mitochondrial calcium stores. On the basis of these data, it is proposed that alterations in calcium metabolism initiated by angiotensin II are exerted not only at the membrane and cytosolic levels but also at the level of the mitochondria. Changes in mitochondrial calcium dynamics may directly contribute to the regulation of mitochondrial steroidogenic enzymes by angiotensin II.