Exchange of Radioactive Magnesium in the Rat.,

Rogers, Terence A.; Mahan, Parker E.

doi:10.3181/00379727-100-24584

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“…Experiments on intact rats Rogers & Mahan (1959) injected 28Mg-labelled MgCl2 I.P. into rats and compared the specific activities of the hearts and plasma as a function of time, using values for the chemical Mg content of rat hearts tabulated in the literature.…”

Section: Resultsmentioning

confidence: 99%

“…It has been reported that, as in other types of muscle (Gilbert, 1960), Mg enters cardiac cells (Rogers & Mahan, 1959;Glaser & Brandt, 1959) and that Mg is transported across the inner membrane of cardiac mitochondria (Brierley, Bachmann & Green, 1962;Brierley, 1967). However, there is no information about the rate of the processes by which Mg enters cardiac cells.…”

Section: Introductionmentioning

confidence: 99%

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Magnesium exchange in rat ventricle

Page¹,

Polimeni²

1972

The Journal of Physiology

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SUMMARY1. The exchange of cellular Mg with external 28Mg in the rat left ventricle was measured in vivo and, under conditions approximating a steady state, in an isolated, working rat heart perfused and contracting at 36-38°C.2. About 98 % of cellular Mg exchanged at a single rate.3. The rate of exchange in vivo was the same as that observed in independent in vitro measurements of the influx and efflux at the physiological external Mg2+ concentration of 0-56 mm. The rate was 0-15 + 0-02 mmole/(kg dry ventricle. min) or 0-21 + 0-02 p-mole/(cm2.seC).4. In the perfused heart the dependence of the influx on the external Mg concentration was hyperbolic with an apparent Vmax of 0-31 + 0-04 mmoles/(kg dry weight. min) and an apparent K_ of 0-57 + 0-08 mM.5. The Mg efflux into a solution containing 2-8 mM-Mg was markedly faster than that into a Mg-free solution.6. These results are interpreted as consistent with a carrier-mediated transport of Mg across the plasma membrane.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Magnesium exchange in rat ventricle

Page¹,

Polimeni²

1972

The Journal of Physiology

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“…The majority of magnesium within cells is, however, usually either bound or is located in intracellular organelles (22,25) such that the concentration of free magnesium ions is relatively low; i.e., 0.3-1.25 mM (29,44,65). Moreover, although intracellular Mg 2ϩ concentration ([Mg 2ϩ ] i ) is regulated, transmembrane fluxes of Mg 2ϩ are invariably slow (24,60,63). As a consequence, under normal conditions, [Mg 2ϩ ] i tends to remain fairly constant.…”

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confidence: 99%

Effects of anoxia, aglycemia, and acidosis on cytosolic Mg²⁺, ATP, and pH in rat sensory neurons

Henrich¹,

Buckler²

2008

American Journal of Physiology-Cell Physiology

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Sensory neurons can detect ischemia and transmit pain from various organs. Whereas the primary stimulus in ischemia is assumed to be acidosis, little is known about how the inevitable metabolic challenge influences neuron function. In this study we have investigated the effects of anoxia, aglycemia, and acidosis upon intracellular Mg(2+) concentration [Mg(2+)](i) and intracellular pH (pH(i)) in isolated sensory neurons. Anoxia, anoxic aglycemia, and acidosis all caused a rise in [Mg(2+)](i) and a fall in pH(i). The rise in [Mg(2+)](i) in response to acidosis appears to be due to H(+) competing for intracellular Mg(2+) binding sites. The effects of anoxia and aglycemia were mimicked by metabolic inhibition and, in a dorsal root ganglia (DRG)-derived cell line, the rise in [Mg(2+)](i) during metabolic blockade was closely correlated with fall in intracellular ATP concentration ([ATP](i)). Increase in [Mg(2+)](i) during anoxia and aglycemia were therefore assumed to be due to MgATP hydrolysis. Even brief periods of anoxia (<3 min) resulted in rapid internal acidosis and a rise in [Mg(2+)](i) equivalent to a decline in MgATP levels of 15-20%. With more prolonged anoxia (20 min) MgATP depletion is estimated to be around 40%. With anoxic aglycemia, the [Mg(2+)](i) rise occurs in two phases: the first beginning almost immediately and the second after an 8- to 10-min delay. Within 20 min of anoxic aglycemia [Mg(2+)](i) was comparable to that observed following complete metabolic inhibition (dinitrophenol + 2-deoxyglucose, DNP + 2-DOG) indicating a near total loss of MgATP. The consequences of these events therefore need to be considered in the context of sensory neuron function in ischemia.

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“…He showed that, 48 hr after the intraperitoneal administration of high specific-activity 28Mg to rats, the specific activity of brain, liver and kidney were equal to one another but higher than that of plasma, whereas the specific activity of skeletal muscle and bone were both less than that of plasma. Rogers & Mahan (1959) also demonstrated the rapid exchange of plasma magnesium with that in liver and kidney. They showed that skeletal muscle contained two pools of magnesium; one which exchanged rapidly with plasma magnesium and one which exchanged more slowly.…”

Section: Analysis Of Resultsmentioning

confidence: 99%

The distribution of exchangeable magnesium within the sheep

Care¹,

Ross²,

Wilson³

1965

The Journal of Physiology

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that after the intravenous administration of 28Mg the decline in the specific activity of the plasma or urinary magnesium can be expressed as the sum of several exponential terms. Two general methods have been proposed for the solution of such a multi-termed equation for the entire system. The choice between these methods is important, since substitution of a single-term exponential equation for a multi-term one will provide erroneously high values for the size of the total exchangeable pool and of the unidirectional exchange rates. This will be demonstrated below.In the first method Care (1960) described the fall in plasma specific activity of magnesium, S(t), with time by the general equation S(t) = Ale klt + A2e-k2t + A3e-kt.He assumed that each term describes the behaviour of magnesium in a different pool and defined the size of each pool Q1, Q2 and Q3 as: injected per unit weight of magnesium. A system was postulated in which the 28Mg moved from one pool to the next successively, homogenization in each pool preceding each step.In the second method, used by Aubert & Milhaud (1960) to describe the time course of the plasma specific activity of calcium in man, the blood was represented as the central pool, the calcium of which exchanges simultaneously with that of three other pools in parallel with it; that is, a mammillary system was postulated with the blood as the central * Present address: The Rowett Research Institute, Bucksburn, Aberdeen.

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Exchange of Radioactive Magnesium in the Rat.,

Cited by 50 publications

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Magnesium exchange in rat ventricle

Magnesium exchange in rat ventricle

Effects of anoxia, aglycemia, and acidosis on cytosolic Mg²⁺, ATP, and pH in rat sensory neurons

The distribution of exchangeable magnesium within the sheep

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Exchange of Radioactive Magnesium in the Rat.,

Cited by 50 publications

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Magnesium exchange in rat ventricle

Magnesium exchange in rat ventricle

Effects of anoxia, aglycemia, and acidosis on cytosolic Mg2+, ATP, and pH in rat sensory neurons

The distribution of exchangeable magnesium within the sheep

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Effects of anoxia, aglycemia, and acidosis on cytosolic Mg²⁺, ATP, and pH in rat sensory neurons