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T E Gunter

Publications and source records attributed to T E Gunter.

47 records · Page 3Linked to original sources
PubMed1976

An electron paramagnetic resonance study of Mn2+ uptake by the chick chorioallantoic membrane.

Mn2+ uptake in the chick chorioallantoic membrane, an embryonic epithelial tissue which transports Ca2+ in vivo was studied using electron paramagnetic resonance (EPR). Mn2+ was used as a paramagnetic analog for Ca2+, since there is evidence that Mn2+ is accumulated by the Ca2+ transport mechanism. After 1.5 h of uptake the EPR spectrum of the Mn2+ in the membrane indicated that 89% of the Mn2+ was in a spin-exchange form, indicating close packing of Mn2+. The Mn2+ spacing was estimated from the line width to be about 4.7 A. The remaining Mn2+ was very likely Mn2+ hexahydrate. At pH 7.4 the spin-exchange spectrum tended to broaden when uptake was inhibited, while at pH 5.0 the spin-exchange spectrum was completely abolished in the presence of inhibitors. The EPR spectrum of Mn2+ in the chorioallantoic membrane had a broader line width than that of Mn2+ in isolated mitochondria, suggesting that in this tissue mitochondria are not directly involved in divalent cation transport. These EPR studies support the concept that divalent cations are sequestered in high concentrations from the rest of the cell contents during transcellular active transport.

Animals↗
PubMed1975

Electron paramagnetic resonance of copper ion and manganese ion complexes with the ionophore A23187.

The binding of Cu2+ and Mn2+ to the ionophore A23187 in chloroform, 90% ethanol, and sonicated phospholipid dispersions in aqueous mediums has been investigated with electron paramagnetic resonance (epr). The spectra indicated axial symmetry for the Cu2+ complexes and distorted octahedral for the Mn2+ complexes. The coordination between metal ion and its ligands is predominantly ionic in character. The stoichiometry, at the concentrations employed, was found to be 1:2 M2+/ionophore except in 90% ethanol where evidence existed for the 1:1 Cu-A23187 complex, as well. Through competition with Mn2+, the sequence of relative affinities in 90% ethanol was measured to be: Mn2+ greater than La3+ greater than Cu2+ greater than Ca2+ greater than Mg2+ greater than Sr2+. The K A of Mn-A23187 binding is greater than 10 10 M-2. In phospholipid dispersions the spectral characteristics of the Cu complex, particularly g, were observed to be a sensitive function of the hydrocarbon chain mobility. This allowed a calculation of the rotational correlation time of the complex to be made. In sonicated dipalmitoyllecithin was computed to be 10-9 sec, reflecting a local viscosity similar to that sensed by the nitroxide spin-label 2,2,6,6-tetramethylpiperidin-1-oxyl. In a (1:1) lecithin-cholesterol dispersion the complex was significantly more immobilized.

Anti-Bacterial Agents↗
PubMed1972

Manganous ion as a spin label in studies of mitochondrial uptake of manganese.

Manganous ion (Mn(2+)) has been used as a spin label for studies of divalent cation uptake by rat liver mitochondria. Spin exchange, observed in the electron paramagnetic resonance (EPR) spectrum of a fraction of the transported Mn(2+), shows that this fraction is bound in regions of high local concentration within the mitochondria. The average separation of manganese ions in that fraction is estimated to be 4.0 +/-0.6 A at the time of greatest concentration.

Animals↗
PubMedDate not supplied

Mitochondrial calcium transport: mechanisms and functions.

Ca(2+)transport across the mitochondrial inner membrane is facilitated by transporters having four distinct sets of characteristics as well as through the Ca(2+)-induced mitochondrial permeability transition pore (PTP). There are two modes of inward transport, referred to as the Ca(2+)uniporter and the rapid mode or RaM. There are also two distinct mechanisms mediating outward transport, which are not associated with the PTP, referred to as the Na(+)-dependent and the Na(+)-independent Ca(2+)efflux mechanisms. Several important functions have been proposed for these mechanisms, including control of the metabolic rate for cellular energy (ATP) production, modulation of the amplitude and shape of cytosolic Ca(2+)transients, and induction of apoptosis through release of cytochrome c from the mitochondrial inter membrane space into the cytosolic space. The goals of this review are to survey the literature describing the characteristics of the mechanisms of mitochondrial Ca(2+)transport and their proposed physiological functions, emphasizing the more recent contributions, and to consider how the observed characteristics of the mitochondrial Ca(2+)transport mechanisms affect our understanding of their functions.

Apoptosis↗
PubMedDate not supplied

Uptake of calcium by mitochondria: transport and possible function.

Vertebrate mitochondria contain a complex system for transport of Ca2+ and related ions, consisting of two saturable modes of Ca2+ influx and two separate, saturable mechanisms of Ca2+ efflux. The characteristics of the mechanisms of Ca2+ uptake, the uniporter and the RaM, are discussed here and suggestions are made about how the mechanisms may work together and separately to mediate the two physiological roles with which they are most commonly associated-control of the rate of cellular ATP production and induction of the permeability transition and apoptosis. It is argued that more subtlety of control of intramitochondrial free Ca2+ concentration ([Ca2+]m) must be used by the uniporter and the RaM to fulfill their physiological roles than has been commonly recognized. This is because an increase in [Ca2+]m is associated with both increased production of ATP which supports the continued life of the cell and with induction of the permeability transition and possibly apoptosis, which leads to cell death. The saturable mechanisms of mitochondrial Ca2+ efflux and the Ca2+-induced mitochondrial permeability transition, which can transport Ca2+ as well as other ions and molecules and is often considered as a Ca2+ transport mechanism, are being reviewed separately.

Animals↗
PubMedDate not supplied

Release of Ca2+ from mitochondria via the saturable mechanisms and the permeability transition.

The literature, reviewed in the previous article, supports three physiological roles for sequestration of calcium by mitochondria: 1) control of the rate of ATP production, 2) activation of the Ca2+-induced mitochondrial permeability transition (PT), and 3) modulation of cytosolic Ca2+ transients. Removal of Ca2+ from mitochondria permits rapid and efficient changes in the rate of ATP production to adapt to changing demands and can reverse the process of PT induction. Two separate, saturable mechanisms for facilitating Ca2+ efflux from mitochondria exist. In addition, the permeability transition or PT, which may also remove Ca2+ from the mitochondrial matrix, is intimately involved in other important functions such as apoptosis. Here we briefly review what is known about these important mitochondrial mechanisms and from their behavior speculate on their possible and probable functions.

Animals↗
PubMedDate not supplied

Manganese and calcium transport in mitochondria: implications for manganese toxicity.

Mn2+ is sequestered by liver and brain mitochondria via the mitochondrial Ca2+ uniporter. The mitochondrial Ca2+ uniporter is a cooperative transport mechanism possessing an external activation site and a transport site. Ca2+ binding to the activation site greatly increases the velocity of uptake of both Ca2+ and Mn2+. Electron paramagnetic resonance (EPR) shows that over 97% of the Mn2+ in the mitochondrial matrix is normally bound to the membrane or to matrix proteins. EPR measurements of manganese within living isolated mitochondria can be repeated for hours, and during this time most of the manganese remains in the Mn2+ state. Mn2+ is transported out of mitochondria via the very slow Na(+)-independent efflux mechanism, which is an active (energy-requiring) mechanism. Mn2+ is not significantly transported over the Na(+)-dependent efflux mechanism, which is the dominant efflux mechanism in heart and brain mitochondria. Mn2+ inhibits the efflux of Ca2+ through both of these efflux mechanisms, having an apparent Ki of 7.9 nmol/mg protein on the Na(+)-independent efflux mechanism and an apparent Ki of 5.1 nmol/mg on the Na(+)-dependent efflux mechanism. Mn2+ inhibition of Ca2+ efflux may increase the probability of the mitochondria undergoing the mitochondrial permeability transition (MPT). Intramitochondrial Mn2+ also inhibits State 3 mitochondrial respiration using either succinate or malate plus glutamate as substrate. The data suggest that Mn2+ depletes cellular energy supplies by interfering with oxidative phosphorylation at the level of the F1ATPase and at much higher concentrations, at Complex I. Effects such as these could lead to apoptosis in active neurons.

Animals↗