Online citations, reference lists, and bibliographies.
← Back to Search

Mechanisms For Intracellular Calcium Regulation In Heart

Antonio Scarpa, Pierpaolo Graziotti

Save to my Library
Download PDF
Analyze on Scholarcy Visualize in Litmaps
Reduce the time it takes to create your bibliography by a factor of 10 by using the world’s favourite reference manager
Time to take this seriously.
Get Citationsy
Initial velocities of energy-dependent Ca++ uptake were measured by stopped-flow and dual-wavelength techniques in mitochondria isolated from hearts of rats, guinea pigs, squirrels, pigeons, and frogs. The rate of Ca++ uptake by rat heart mitochondria was 0.05 nmol/mg/s at 5 µM Ca++ and increased sigmoidally to 8 nmol/mg/s at 200 µM Ca++. A Hill plot of the data yields a straight line with slope n of 2, indicating a cooperativity for Ca++ transport in cardiac mitochondria. Comparable rates of Ca++ uptake and sigmoidal plots were obtained with mitochondria from other mammalian hearts. On the other hand, the rates of Ca++ uptake by frog heart mitochondria were higher at any Ca++ concentrations. The half-maximal rate of Ca++ transport was observed at 30, 60, 72, 87, 92 µM Ca++ for cardiac mitochondria from frog, squirrel, pigeon, guinea pig, and rat, respectively. The sigmoidicity and the high apparent Km render mitochondrial Ca++ uptake slow below 10 µM. At these concentrations the rate of Ca++ uptake by cardiac mitochondria in vitro and the amount of mitochondria present in the heart are not consistent with the amount of Ca++ to be sequestered in vivo during heart relaxation. Therefore, it appears that, at least in mammalian hearts, the energy-linked transport of Ca++ by mitochondria is inadequate for regulating the beat-to-beat Ca++ cycle. The results obtained and the proposed cooperativity for mitochondrial Ca++ uptake are discussed in terms of physiological regulation of intracellular Ca++ homeostasis in cardiac cells.