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Biomedical subjects

E Carafoli

Publications and source records attributed to E Carafoli.

At least 289 records · Page 16Linked to original sources
PubMed1978

The interrelations between the transport of sodium and calcium in mitochondria of various mammalian tissues.

Addition of ruthenium red to mitochondria isolated from brain, adrenal cortex, parotid gland and skeletal muscle inhibits further uptake of Ca2+ by these mitochondria but induces little or no net Ca2+ efflux; the further addition of Na+, however, induces rapid efflux of Ca2+. The velocity of the Na+-induced efflux of Ca2+ from these mitochondria exhibits a sigmoidal dependence on the [Na+]. Addition of Na+ to mitochondria exhibiting the most active Na+-dependent efflux of Ca2+ (brain and adrenal cortex) also releases Ca2+ in the absence of ruthenium red and, under these conditions, the mitochondria become uncoupled. It is concluded that the efflux of Ca2+ from these mitochondria occurs via a Na+-dependent pathway, possibly a Na+-Ca2+ antiporter, that is distinct from the ruthenium-red-sensitive carrier that catalyses energy-linked Ca2+-influx. The possible role of the Na+-dependent efflux process in the distribution of Ca2+ between the mitochondria and the cytosol is discussed. In contrast, mitochondria from liver, kidney, lung, uterus muscle and ileum muscle exhibit no Na+-dependent efflux of Ca2+.

Animals↗
PubMed1977

Ca2+ transport mediated by a synthetic neutral Ca2+ -ionophore in biological membranes.

The effect of a synthetic neutral ligand on the Ca2+ permeability of several biological membranes has been investigated. The ligand had been previously shown to possess Ca2+ -ionophoric activities in artificial phospholipid membranes. The neutral ionophore is able to transport Ca2+ across the membranes of erythrocytes and sarcoplasmic reticulum, when lipophilic anions such as tetraphenylborate and carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP) are present, presumably to facilitate the diffusion of the charged Ca2+ -ionophore complex across the hydrophobic core of the membrane. In mitochondria, the neutral ionophore promotes the active transport of Ca2+ in response to the negative membrane potential generated by respiration, in the presence of the specific inhibitor of the natural carrier ruthenium red.

Animals↗
PubMed1977

The translocation of Ca2+ across phospholipid bilayers induced by a synthetic neutral Ca2+ -ionophore.

The effect of a neutral synthetic Ca2+ -ligand, which induces selective Ca2+ transport in electrodialysis experiments in bulk membranes, on the Ca2+ permeability of phospholipid bilayers has been investigated. The ligand is able to promote the transport of Ca2+ across synthetic phospholipid bilayers and can therefore be classified as a Ca2+ -ionophore. Its activity is enhanced by the uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP). The efficiency of the neutral carrier-mediated Ca2+ transport is rather low as compared with that of the charged Ca2+ -ionophore X537A. The Ca2+ selectivity of the nuetral ionophore is decreased by its incorporation in the low dielectric ambient of the phospholipid bilayer.

Biological Transport, Active↗
PubMed1976

Calcium regulation in heart cells. The interaction of mitochondrial and sarcoplasmic reticulum with troponin-bound calcium.

A study has been carried out of the interaction of dog heart mitochondria and sarcoplasmic reticulum with Ca2+ bound to troponin or to its Ca2+-binding component (troponin-C). Both organelles are able to release more than 80% of the Ca2+ bound to the two proteins. However, sarcoplasmic reticulum is only able to do so in the presence of oxalate, whereas mitochondria are active also in the absence of permeant Ca-complexing anions. On the other hand, calcium uptake in heart mitochondria is severely inhibited by Mg2+. The results are discussed with reference to the problem of the control of Ca2+ in heart sarcoplasm.

Animals↗
PubMed1976

Respiration-dependent efflux of magnesium ions from heart mitochondria.

Energy-linked respiration causes a net movement of Mg2+ between rat heart mitochondria and the ambient medium. When the extramitochondrial concontration of Mg2+ is less that about 2.5 mM the net movement of Mg2+ constitutes an efflux, whereas a net influx of Mg2+ occurs when the external concentration of Mg2+ is greater than this. Both the efflux and the influx are induced to only a very small degree by externally added ATP. Evidence suggests that Pi may be required for the respiration-induced efflux of Mg2+.

Adenosine Diphosphate↗
PubMed1975

Aspects of energy-linked calcium accumulation by rat heart mitochondria.

When intact rat heart mitochondria were pulsed with 150 nmol of CaCl2/mg of mitochondrial protein, only a marginal stimulation of the rate of oxygen consumption was observed. This result was obtained with mitochondria isolated in either the presence or absence of nagarse. In contrast, rat liver mitochondria under similar conditions demonstrated a rapid, reversible burst of respiration associated with energy-linked calcium accumulation. Direct analysis of calcium retention using 45Ca and Millipore filtration indicated that calcium was accumulated by heart mitochondria under the above conditions via a unique energy-dependent process. The rate of translocation by heart mitochondria was less than that of liver mitochondria; likewise the release of bound calcium back into the medium was also retarded. These results suggest that the slower accumulation and release of calcium is characteristic of heart mitochondria. The amound of calcium bound was independent of penetrant anions at low calcium concentrations. Above 100 nmol/mg of mitochondrial protein, the total calcium bound was increased by the presence of inorganic phosphate. Under nonrespiring conditions, a biphasic Scatchard plot indicative of binding sites with different affinities for Ca2+ was observed. The extrapolated constants are 7.5 nmol/mg bound with an apparent half-saturation value of 75 muM and 42.5 nmol/mg bound with half-saturation at 1.15 mM. The response of the reduced State 4 cytochrome b to pulsed additions of Ca2+ was used to calculate an energy-dependent half-saturation constant of 40 muM. When the concentration of free calcium was stabilized at low levels with Ca2+-EGTA buffers, the spectrophotometrically determined binding constant decreased two orders of magnitude to an apparent affinity of 4.16 X 10(-7) M. Primary of calcium transport over oxidative phosphorylation was not observed with heart mitochondria. The phosphorylation of ADP competed with Ca2+ accumulation, depressed the rates of cation transport, and altered the profile of respiration-linked H+ movements. Consistent with these result was the observation that with liver mitochondrial the magnitude of the cytochrome b oxidation-reduction shift was greater for Ca2+ than for ADP, whereas calcium responses never surpassed the ADP response in heart mitochondria. Furthermore, Mg2+ ingibited calcium accumulation by heart mitochondria while having only a slight effect upon calcium transport in liver mitochondria. The unique energetics of heart mitochondrial calcium transport are discussed relative to the regulated flux of cations during the cardiac excitation-relaxation cycle.

Adenosine Diphosphate↗