Ion Transport in Liver Mitochondria

Rossi, C.S.; Azzi, Angelo; Azzone, Giovanni

doi:10.1016/s0021-9258(18)96216-2

Cited by 85 publications

(3 citation statements)

References 5 publications

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“…Further support is provided by the observation that the charge stoichiometry is 2 K+/Ca2+ in the case of the K+ diffusion driven process and 2 H+/Ca2+ for the H+ pump driven process (Azzone & Azzi, 1966;Rossi et al, 1967;Azzone et al, 1977b;Reynafarje & Lehninger, 1977). K+ diffusion driven Ca2+ transport possesses some limitation with respect to H+ pump driven transport: (a) only initial kinetics and not steady-state kinetics can be analyzed; (b) the effect of high [K+]0 cannot be analyzed; and (c) the dimension of the K+ gradient decreases with aging since mitochondrial storage is accompanied by K+ leakage.…”

Section: Resultsmentioning

confidence: 95%

“…K+ gradient has been used to drive energy-requiring reactions in several instances; (a) Ca2+ uptake (Azzone & Azzi, 1966;Rossi et al, 1967;Scarpa & Azzone, 1970); (b) ATP synthesis (Cockrell et al, 1967;Rossi & Azzone, 1970; Azzone & Massari, 1971); (c) reversal of electron transport (Cockrell et al, 1967;Conover, 1971). Ca2+ translocation in mitochondria is generally accepted to take place via a native carrier.…”

Section: Resultsmentioning

confidence: 99%

“…The rate of Ca2+ influx into rotenone-treated mitochondria has been measured by recording with a K+ electrode the rate of K+ efflux following the addition of valinomycin (Azzone & Azzi, 1966;Rossi et al, 1967;Scarpa & Azzone, 1970). The rate of K+ efflux was then calculated by taking into account the logarithmic response of the electrode.…”

Section: Methodsmentioning

confidence: 99%

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Kinetics of calcium(2+) ion carrier in rat liver mitochondria

Bragadin¹,

Pozzan²,

Azzone³

1979

Biochemistry

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139

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The rate of aerobic Ca2+ transport is limited by the rate of the H+ pump rather than by the Ca2+ carrier. The kinetics of the Ca2+ carrier has therefore been studied by using the K+ diffusion potential as the driving force. The apparent Vmax of the Ca2+ carrier is, at 20 degrees C, about 900 nmol (mg of protein)-1 min-1, more than twice the rate of the H+ pump. The apparent Vmax is depressed by Mg2+ and Li+. This supports the view that the electrolytes act as noncompetitive inhibitors of the Ca2+ carrier. The degree of sigmoidicity of the kinetics of Ca2+ transport increases with the lowering of the temperature and proportionally with the concentration of impermeant electrolytes such as Mg2+ and Li+ but not choline. The effects of temperature and of electrolyte do not support the view that the sigmoidicity is due to modifications of the surface potential. Rather, they suggest that Ca2+ transport occurs through a multisubunit carrier, where cooperative phenomena are the result of ligand-induced conformational changes due to the interaction of several allosteric effectors with the carrier subunits. In contrast with La3+ which acts as a competitive inhibitor, Ruthenium Red affects the kinetics by inducing phenomena both of positive and of negative cooperativity. The Ruthenium Red induced kinetics has been reproduced through curve-fitting procedures by applying the Koshland sequential interaction hypothesis to a four-subunit Ca2+ carrier model.

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Section: Resultsmentioning

confidence: 95%

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Kinetics of calcium(2+) ion carrier in rat liver mitochondria

Bragadin¹,

Pozzan²,

Azzone³

1979

Biochemistry

Self Cite

139

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A comparative study of the role of mitochondria and the sarcoplasmic reticulum in the uptake and release of Ca⁺⁺ by the rat diaphragm

Carafoli

Patriarca

Rossi

1969

Journal Cellular Physiology

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The respective importance of mitochondria and of sarcoplasmic reticulum in the uptake and maintenance of C a + + by the isolated rat diaphragm has been compared. Diaphragms were incubated a t 30" in conditions optimal for Ca++ uptake either by isolated mitochondria or by sarcoplasmic reticulum: more Ca++ was taken up from the "mitochondrial" medium. For maximal uptake, Pi and Mg++ were necessary; substitution of NaCl and KCI with sucrose had no effect on the uptake. The uptake was markedly inhibited by uncouplers of oxidative phosphorylation, by respiratory inhibitors, and by lowering the temperature of the incubation medium to 0"; it was not affected by oligomycin, aurovertin, DCCD, nor by inhibitors of Ca+ + transport in the isolated sarcoplasmic reticulum (ergotamine, ergobasinine, caffeine). The lack of effect of caffeine was not due to lack of penetration into the muscle. Permeability barriers for ergotamine and ergobasinine could not be excluded. The maintenance of Ca++ by the diaphragm was optimal in a medium containing Pi and Mg+ +. Uncoupling agents and respiratory inhibitors accelerated the rate and extent of release of Ca++ by the diaphragm. Lowering the temperature of the incubation medium to O", or addition of oligomycin, aurovertin, DCCD, had no effect on the release. The release of C a + + was also unaffected by ergotamine, ergobasinine, caffeine. The results suggest a role for mitochondria in the uptake and maintenance of Ca+ + by the isolated diaphragm.

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