Purpose An excessive accumulation of intracellular Ca2+ occurs in diverse tissues, including the heart, in rats with aldosterone/salt treatment. This Ca2+ overloading includes total intracellular Ca2+ (both organellar and cytosolic compartments) as well as cytosolic-free [Ca2+]i and mitochondrial-free [Ca2+]m. It may occur as a result of parathyroid hormone receptor-mediated Ca2+ entry as a result of the associated secondary hyperparathyroidism or with aldosterone-mediated increased expression of L-type Ca2+ channels. The distribution of the increased intracellular Ca2+ in aldosteronism that influences mitochondrial and cytosolic compartments remains to be elucidated.
Methods and Results Herein we monitored cytosolic-free Ca2+ in cardiomyocytes harvested from isolated rat hearts perfused with collagenase and intramitochondrial Ca2+ in mitochondria isolated by differential centrifugation. Cells and isolated mitochondria were each loaded with Fura-2, a Ca2+-sensitive probe, with fluorescence monitored by spectrophotometer. The purity of mitochondria was assessed by flow cytometry with mitochondria-specific dye MitoTracker Red. There were four experimental groups: age-/gender-matched controls (C); 4 weeks aldosterone (0.75 μg/h) plus 1% NaCl in drinking water (A); 4 weeks A + spironolactone (S, 150 mg/kg/d by gavage); and 4 weeks A + amlodipine (CCB, 5 mg/kg/d by gavage). We found (p < .05, *A vs C, †A + S vs A, ‡A + CCB vs A):
Conclusions Both [Ca2+]m and [Ca2+]i rose in cardiomyocytes harvested from rats with aldosteronism. The rise in [Ca2+]m was concordant with the rise in [Ca2+]i and could be prevented by S but was not altered by CCB cotreatment. The functional significance of these iterations in cardiomyocyte Ca2+ remains to be elucidated and may impact on the redox state of these cells and the electrical behavior of the heart.
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