Mg2+ and the permeability of heart mitochondria to monovalent cations

Wehrle, Janna P.; Jurkowitz, Marianne S.; Scott, K.M.; Brierley, Gerald P.

doi:10.1016/0003-9861(76)90350-7

Cited by 70 publications

(17 citation statements)

References 38 publications

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“…7), whereas removing by EDTA of Mg 2+, loosly bound to the inner membrane (22), results in acceleration of swelling. 7), whereas removing by EDTA of Mg 2+, loosly bound to the inner membrane (22), results in acceleration of swelling.…”

Section: Discussionmentioning

confidence: 99%

“…Other assay conditions are described in methods section.another assay medium than for analysis of oxidative phosphorylation in order to compare our results with those of other authors(6,13,17,22). Other assay conditions are described in methods section.another assay medium than for analysis of oxidative phosphorylation in order to compare our results with those of other authors(6,13,17,22).…”

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confidence: 93%

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The role of ATP and lactic acid for mitochondrial function during myocardial ischemia

et al. 1979

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Phosphorylation rates of canine heart mitochondria isolated after various periods of myocardial ischemia after cardioplegic arrest were correlated with the myocardial ATP-, lactate- and undissociated lactic acid content as well as with interstitial H+-concentration. The following correlation coefficients were found: ATP: 0.87, lactate: 0.93, interstitial H+: 0.73. The calculated undissociated lactic acid content and the mitochondrial phosphorylation rate during ischemia showed a correlation coefficient of r = 0.95. Swelling measurements of mitochondria, isolated immediately after cardioplegic arrest, demonstrated that an undissociated lactic acid- and an ATP-concentration of 70 microM and 28 microM respectively are necessary for a half maximal swelling reaction under anaerobic conditions. The results suggest that the accumulation of undissociated lactic acid during myocardial ischemia could play an important role for mitochondrial damage in vivo.

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Section: Discussionmentioning

confidence: 99%

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confidence: 93%

The role of ATP and lactic acid for mitochondrial function during myocardial ischemia

et al. 1979

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“…1A) into a small shrinkage. Apparently, "tightening" the membranes with Mg2+ retards electrophoretic K+ entry (14), and the effect of acidification is now manifest in solute efflux. We added Mg2+ in all subsequent experiments to reduce the possibility that acidification was primarily making membranes leaky.…”

Section: Methodsmentioning

confidence: 99%

“…Acidification is potentially capable of removing surface-bound cations in exchange for H+, and Wehrle et al (14) have shown that membrane permeability in heart mitochondria is increased by removal of a small amount of superficially bound Mg2+. Fig.…”

Section: Methodsmentioning

confidence: 99%

Activation of Endogenous Respiration and Anion Transport in Corn Mitochondria by Acidification of the Medium

Kimpel¹,

Hanson²

1977

Plant Physiol.

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Acdification of the suspending medium of corn mitocbondrina (Zea mays L., WF9 x Mol7) from pH 7.5 to pH 6.8 to 6.4 It has been reported (6) that corn mitochondria show pronounced contraction or shrinkage as judged by light transmission when the medium is acidified. There were indications that certain anions, such as citrate or acetate, opposed the acid contraction, suggesting salt uptake driven by the pH gradient. However, in terms of Mitchell's chemiosmotic hypothesis (9) this should not happen. Net salt uptake requires a proton motive force (Ap = Ai -59ApH, mV at 25 C) with At# driving cation uptake as an electrophoretic uniport, and ApH driving anion uptake as a neutral symport or antiport. Simply acidifying the medium does not provide the requisite electrical potential.We have investigated this problem using sulfate, phosphate, and citrate as transportable anions. Acidification of the medium by about 1 pH unit does produce osmotic swelling, but the transport is primarily due to activation of endogenous respiration. MATERIALS AND METHODSMitochondria were isolated from corn shoots (Zea mays L. WF9 x Mol7) essentially as previously described (6), but with the isolation medium changed to 0.4 M sucrose, 50 mm TES buffer, 1 mg/ml of BSA, 3 mm EDTA, 3 mM MgCl2, adjusted to pH 7.6 with KOH. Final suspension was in 0.25 M sucrose plus 1 mg/ml of BSA.Measurements of per cent transmission, pH, and 02 were as previously described (6) but at room temperature (23 C). Full scale transmittance was set from 20 to 40%, adjusting slit width to bring initial transmittance to 30%. Cuvettes contained 4 ml of aerated 100 mm sucrose, 10 mm TES, 1 mg/ml of BSA, adjusted to pH 7.5; however, after addition of 0.7 to 1 mg of ' Supported by United States Energy Research and DevelopmentAdministration Grant E-(11-1)-790. mitochondrial protein the actual pH recorded was sometimes as low as 7.4. Additions of acids and salts to the medium were from 1 M stock solutions. Where pH recordings were not made (see Fig. 2) the amount of acid to be added, especially in the presence of phosphate and citrate, was determined separately.RESULTS AND DISCUSSION Figure 1A shows the effect of acidifying the medium with H2SO4 on the light transmission of the mitochondrial suspension. There is close correspondence between osmotic swelling as measured by per cent transmission (% T) and osmotic theory (7, 11), and assuming that this holds over the neutral pH range (pH 6-8), addition of H2S04 initiates a slow osmotic swelling. Dropping the pH to 4.3 causes an abrupt "shrinkage" which slows after a few sec and takes several min to stabilize. The transition point between swelling and shrinkage was in the range of pH 5.8 to 6. Shrinkage was secured using several acids and it may represent a physical response of membrane or matrix proteins to high proton concentration rather than solute efflux driven by an acid gradient. Previous investigations, however, showed a loss of mitochondrial water at low pH (6). We limited the present investigation to the swelling...

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“…We have found that the acidic ionophore A-23187 is the reagent par excellence for depletion of coupled mitochondria to the point at which a cation requirement for uncoupling is demonstrable (22). The action of A-23187 can be duplicated by EDTA (23) experiments of this kind. First, uncoupler-mediated release of respiration can be potentiated by either monovalent or divalent cations.…”

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confidence: 99%

Uncouplers and the molecular mechanism of uncoupling in mitochondria.

Kessler¹,

Zande²,

Tyson³

et al. 1977

Proc. Natl. Acad. Sci. U.S.A.

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Uncouplers are molecules with protonophoric and ionophoric capabilities that mediate coupled cyclical transport of cations-a transport that takes precedence over all other coupled processes. Uncouplers form cation-containing complexes with electrogenic ionophores that potentiate cyclical transport of cations. The molecular mechanism of uncoupling sheds strong light on the mechanism of coupling. Electron flow in mitochondria can drive synthesis of ATP, accumviation of cations (K+, Mg2+, Ca2+), or transfer of hydrogen from NADPH to NAD+. Uncouplers sever the link between the driving reaction and the driven reactions without suppressing the rate of electron flow (1-3). The same effect of uncoupler on coupled reactions is observed when the driving reaction is hydrolysis of ATP rather than electron flow. This phenomenon of uncoupling is the most characteristic feature of mitochondrial energy coupling, and, although discovered some 30 years ago (3), its molecular mechanism has been an enigma. One valuable hint about the action of uncouplers has come to light. Under the conditions in which uncoupling takes place, all protonic and cationic gradients are abolished (4, 5)-an indication that uncouplers are carriers of both protons and cations.There are 20 to 30 different molecular species that have in common the property of suppressing all coupled processes whether driven by electron flow or hydrolysis of ATP and the property of being equally effective in these two respects regardless of the substrate used for electron flow or the nature of the coupling site (6, 7). They differ only in respect to the concentration at which uncoupling is maximal. The most efficient uncouplers such as SF6847 can uncouple in the nanomolar range, whereas the less efficient uncouplers such as pentachlorophenol and 2,4-dinitrophenol are effective only in the millimolar range.Uncoupling by the combination of valinomycin and nigericin in presence of K+ It has been known for some time that the combination of two ionophores (valinomycin and'nigericin) can uncouple oxidative phosphorylation in the same fashion as do classical uncouplers but only in the presence of K+ (8, 9). We considered this correspondence of action as an invaluable clue since it has already been established that the combination of valinomycin and nigericin induces cyclical transport of K+ coupled to electron flow (Fig. 1). The critical question was whether this combination of ionophores could duplicate all the known properties of uncouplers. The data of Table 1). Uncouplers as protonophores and ionophores The prevailing dogma that uncouplers uncouple by virtue of collapsing a proton gradient has spawned a vast literature attesting to the protonophoric capability of uncouplers (17-19), and hence this capability has been most thoroughly documented and verified. All uncouplers, without exception, can dissociate a proton in their uncharged state and can take up a proton in their charged state in the pH range of uncoupler action. In general, the best uncouplers have a pK above...

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Mg2+ and the permeability of heart mitochondria to monovalent cations

Cited by 70 publications

References 38 publications

The role of ATP and lactic acid for mitochondrial function during myocardial ischemia

The role of ATP and lactic acid for mitochondrial function during myocardial ischemia

Activation of Endogenous Respiration and Anion Transport in Corn Mitochondria by Acidification of the Medium

Uncouplers and the molecular mechanism of uncoupling in mitochondria.

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