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Biomedical subjects

M Crompton

Publications and source records attributed to M Crompton.

At least 55 records · Page 3Linked to original sources
PubMed1985

Ca2+-dependent inhibition by trifluoperazine of the Na+-Ca2+ carrier in mitoplasts derived from heart mitochondria.

The interaction of trifluoperazine and extramitochondrial Ca2+ with the heart mitochondrial Na+-Ca2+ carrier has been investigated. External Ca2+ inhibits the carrier equally in mitochondria and mitoplasts in which the outer membrane is lysed. Sensitivity to Ca2+ is not removed by washing mitoplasts under varied conditions. Trifluoperazine is a potent inhibitor of the carrier in mitoplasts but not in mitochondria. Trifluoperazine inhibition in mitoplasts depends markedly on the presence of extramitochondrial Ca2+ (2 microM).

Animals↗
PubMed1985

Aspirin prevents carbamylation of soluble lens proteins and prevents cyanate-induced phase separation opacities in vitro: a possible mechanism by which aspirin could prevent cataract.

The carbamylation of lens proteins by cyanate causes conformational changes, and cyanate causes cataract. There is some evidence that aspirin is beneficial to cataract patients, so its effect on the carbamylation of lens proteins and on opacification produced by cyanate in vitro was studied. Aspirin decreased the phase separation temperature in lenses exposed to cyanate, and was found to reduce the rate of carbamylation of most, if not all, soluble lens proteins. Studies with radiolabelled aspirin lead to the conclusion that the drug achieves this protection by chemically modifying the proteins. The nature of this modification and the relevance of these results to human cataract is discussed.

Animals↗
PubMed1983

The alpha-adrenergic-mediated activation of the cardiac mitochondrial Ca2+ uniporter and its role in the control of intramitochondrial Ca2+ in vivo.

Administration of methoxamine (10 microM, 2 min) to perfused rat hearts increased the rate at which subsequently isolated mitochondria accumulated Ca2+. Methoxamine did not change significantly the development of delta phi with time or the basal rates of Ca2+ flux on inhibition of the uniporter with Ruthenium Red. With 200 microM-Pi, the rates of Ca2+ uptake at constant delta phi were unaffected by the small variations in endogenous [Pi] between mitochondrial preparations, and were also unaffected by changes in internal Ca2+ over the approximate range 8-43 nmol of Ca2+/mg. At low internal Ca2+ (about 8 nmol/mg of protein) the rates of Ca2+ uptake at constant delta phi were unaffected by addition of 200 microM-Pi. Under these conditions, the uniporter activity and the uniporter conductance were increased by 38-40% by methoxamine pretreatment. The endogenous Ca2+ content of mitochondria from control heart was about 1.8 nmol of Ca2+/mg of protein. Perfusion with agonist increased the Ca2+ content as follows: 10 microM-methoxamine (2 min), 48%; 1 microM-isoprenaline (2 min), 100%; 1 microM-adrenaline (2 min), 140%. The implications of the data for the adrenergic control of oxidative metabolism by intramitochondrial Ca2+ is discussed.

Animals↗
PubMed1983

The activation of Na+-dependent efflux of Ca2+ from liver mitochondria by glucagon and beta-adrenergic agonists.

The Na+-induced efflux of Ca2+ from liver mitochondria was activated by tissue pretreatment with 1 microM-adrenaline, 1 microM-isoprenaline, 10 nM-glucagon and 100 microM-cyclic AMP when 10 mM-lactate plus 1 mM-pyruvate were present in the perfusion medium. Infusion of the alpha 1-adrenergic agonist, phenylephrine (10 microM), was ineffective. The activation induced by the beta-adrenergic agonist, isoprenaline, was maximal after infusion of agonist for 2 min. The isoprenaline-induced activation was very marked (120-220%), with about 7 nmol of intramitochondrial Ca2+/mg of protein, but was not evident with greater than 15 nmol of Ca2+/mg. Ca2+ efflux in the absence of Na+ and in the presence of the Ca2+ ionophore A23187 was not affected by isoprenaline pretreatment over the range 6-23 nmol of internal Ca2+/mg. With 10 mM-lactate plus 1 mM-pyruvate in the perfusion medium, glucagon and isoprenaline infusion increased tissue cyclic AMP content about 8-fold and 3-fold respectively. With 10 mM-pyruvate alone, neither glucagon nor isoprenaline caused a significant increase in cyclic AMP. Omission of lactate also abolished the ability of glucagon, but not of isoprenaline, to activate the Na+-induced efflux of Ca2+. The data indicate that cyclic AMP may mediate the activation caused by glucagon, but provide no evidence that cyclic AMP is an obligatory link in the beta-adrenergic-induced activation.

Adrenergic beta-Agonists↗
PubMed1983

The sequestration of Ca2+ by mitochondria in rat heart cells.

Rat heart ventricular cells, purified by Percoll density gradient centrifugation, were incubated in the presence of 1.3 mM CaCl2. After 20 min incubation, samples of the cells were lysed in medium containing 0.3 mM digitonin, ruthenium red and EGTA, and a mitochondrial fraction was isolated at intervals thereafter. Extrapolation of the mitochondrial 45Ca2+ contents to zero time enabled the endogenous 45Ca2+ to be estimated at the time of cell lysis. The lysis conditions yielded essentially complete release of lactate dehydrogenase from the cells, but caused negligible damage to the mitochondria as judged by their retention of glutamate dehydrogenase, and their ability to accumulate and retain Ca2+ in the absence of ruthenium red and EGTA. The data indicate that about 13% of total cell Ca2+ only may be mitochondrial in vivo.

Animals↗
PubMed1982

Evidence for beta-adrenergic activation of Na+-dependent efflux of Ca2+ from isolated liver mitochondria.

The existence of a Na(+)-dependent mechanism for Ca(2+) efflux from isolated rat liver mitochondria was confirmed. The activity of this system is decreased by 60% in mitochondria isolated from perfused livers. The Na(+)-dependent activity is fully restored by infusion of either 1mum-adrenaline or 1mum-isoprenaline, but the alpha-adrenergic agonist phenylephrine is ineffective.

Animals↗
PubMed1982

Evidence for the existence of regulatory sites for Ca2+ on the Na+/Ca2+ carrier of cardiac mitochondria.

The Na+-induced efflux of Ca2+ catalysed by the Na+/Ca2+ carrier of cardiac mitochondria is strongly inhibited by extramitochondrial Ca2+. The nature of this inhibition was investigated as follows. (a) The apparent association of external Na+ and the Ca2+ analogue Sr2+ with substrate-binding sites (i.e. those sites involved in cation translocation) is promoted markedly by K+. The inhibition of Na+/Ca2+ exchange by external Ca2+ is affected little by K+. (b) There is a competitive relationship between the binding of external Na+ and external Ca2+ to substrate-binding sites, whereas at low concentrations (less than 4 microM) extramitochondrial Ca2+ is a partial non-competitive inhibitor with respect to external Na+. (c) This inhibiton by external Ca2+ is characterized by a maximal decrease of about 70% in the Vmax of Na+/Ca2+ exchange and by cooperative binding of external Ca2+ to sites that are half saturated by 0.7-0.8 microM free Ca2+. The binding of Ca2+ and Sr2+ to substrate-binding sites shows no co-operativity. These criteria suggest that the Na+/Ca2+ carrier may contain regulatory sites that render the carrier sensitive to changes in extramitochondrial [Ca2+] within the physiological range.

Animals↗
PubMed1981

The alpha-adrenergic-mediated activation of Ca2+ influx into cardiac mitochondria. A possible mechanism for the regulation of intramitochondrial free CA2+.

Mitochondria isolated from rat hearts perfused with adrenaline, and from hearts excised from adrenaline-treated rats, showed an enhanced rate of respiration-dependent Ca2+ uptake. Adrenaline pretreatment did not change the activity of the Na+/Ca2+-antiporter of isolated heart mitochondria. Simultaneous measurements of the membrane potential revealed that perfusion with adrenaline has no significant effect on this parameter during Ca2+ accumulation. The activation of Ca2+ uptake was induced also by the alpha-adrenergic agonist, methoxamine, but not by the beta-adrenergic agonist, isoprenaline. Methoxamine pretreatment also increased the sensitivity of alpha-oxoglutarate dehydrogenase in intact mitochondria to 10 nM--300 nM extramitochondrial Ca2+ during steady-state Ca2+ recycling across the inner membrane. Possible implications of these data for the adrenergic regulation of oxidative metabolism are discussed.

Animals↗
PubMed1980

The role of inorganic phosphate in the release of Ca2+ from rat-liver mitochondria.

The effect of inorganic phosphate on Ca2+ retention has been investigated using phosphate-depleted liver mitchondria. Phosphate induces the release of Ca2+ through an efflux route insensitive to ruthenium red. This effect is not due to functional or structural damage, since mitochondria maintain their membrane potential during phosphate-induced Ca2+ efflux. Direct enzymatic measurement of mitochondria pyridine nucleotides has established that changes in their redox state (i.e. increased oxidation) do not play a role in the phosphate-effect. The phosphate-induced Ca2+ efflux requires transport of phosphate out of mitochondria. However, the fluxes of Ca2+ and phosphate do not coincide: the release of phosphate preceeds that of Ca2+.

Animals↗
PubMed1978

The cycling of calcium, sodium, and protons across the inner membrane of cardiac mitochondria.

A method is described that permits simultaneous determination of the net charge transfer associated with Ca2+ transport by the ruthenium-red-sensitive carrier and the ionized internal [Ca2+] in heart mitochondria. The data indicate that this carrier catalyses a charge-uncompensated flux of Ca2+. Full charge compensation for Ca2+ influx is provided by the respiration-dependent efflux of H+. The net efflux of Ca2+ induced by Na+ is analysed in terms of two other carriers, a Na+-Ca2+ antiporter and a Na+-H+ antiporter. Evidence is presented that these two carriers are separate and that the Na+-H+ exchange is the more rapid. The fluxes of Ca2+, Na+ and H+ during the Na+-induced efflux of Ca2+ support a series of events in which the Na+-H+ exchange enables unidirectional Ca2+ fluxes via the uniport and antiport systems to be integrated into a cycle.

Animals↗