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Saturable Mechanism (saturable + mechanism)

Distribution by Scientific Domains

Life Sciences	100%

Selected Abstracts

Release of Ca 2+ from Mitochondria via the Saturable Mechanisms and the Permeability Transition

IUBMB LIFE, Issue 3-5 2001
Douglas R. Pfeiffer
Abstract 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 Ca 2+ -induced mitochondrial permeability transition (PT), and 3) modulation of cytosolic Ca 2+ transients. Removal of Ca 2+ 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 Ca 2+ efflux from mitochondria exist. In addition, the permeability transition or PT, which may also remove Ca 2+ 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. [source]

Kinetics of Thyroxine (T4) and Triiodothyronine (T3) Transport in the Isolated Rat Heart

EXPERIMENTAL PHYSIOLOGY, Issue 1 2001
Mirko A. Rosic
The dynamics and kinetics of thyroid hormone transport in the isolated rat heart were examined using the modified unidirectional paired tracer dilution method. The uptake of 125I-thyroxine (125I-T4) and 125I-triiodothyronine (125I-T3) from the extracellular space into heart cells was measured relative to the extracellular space marker 3H-mannitol. The thyroid hormone maximal uptake was 54.4% for 125I-T4 and 52.15% for 125I-T3. The thyroid hormone net uptake was 25.69% for 125I-T4 and 25.49% for 125I-T3. Backflux from the intracellular space was 53.17% for 125I-T4 and 61.59% for 125I-T3. In the presence of unlabelled thyroid hormones, 125I-T4 and 125I-T3 maximal uptakes were reduced from 10.1 to 59.74% and from 34.6 to 65.3%, respectively, depending on the concentration of the unlabelled hormone, suggesting a saturable mechanism of the thyroid hormone uptake by the heart cells, with Km(T4)= 105.46 ,M and the maximal rate of 125I-thyroid hormone flux from the extracellular space to heart cells (Vmax(T4)) = 177.84 nM min,1 for 125I-T4 uptake, and Km(T3)= 80.0 ,M and Vmax(T3)= 118.5 nM min,1 for 125I-T3 uptake. [source]

Post-transcriptional suppression of pathogenic prion protein expression in Drosophila neurons

JOURNAL OF NEUROCHEMISTRY, Issue 6 2003
Nathan R. Deleault
Abstract A wealth of evidence supports the view that conformational change of the prion protein, PrPC, into a pathogenic isoform, PrPSc, is the hallmark of sporadic, infectious, and inherited forms of prion disease. Although the central role played by PrPSc in the pathogenesis of prion disease is appreciated, the cellular mechanisms that recognize PrPSc and modulate its production, clearance, and neural toxicity have not been elucidated. To address these questions, we used a tissue-specific expression system to express wild-type and disease-associated PrP molecules heterologously in Drosophila melanogaster. Our results indicate that Drosophila brain possesses a specific and saturable mechanism that suppresses the accumulation of PG14, a disease-associated insertional PrP mutant. We also found that wild-type PrP molecules are maintained in a detergent-soluble conformation throughout life in Drosophila brain neurons, whereas they become detergent-insoluble in retinal cells as flies age. PG14 protein expression in Drosophila eye did not cause retinal pathology. Our work reveals the presence of mechanisms in neurons that specifically counterbalance the production of misfolded PrP conformations, and provides an opportunity to study these processes in a model organism amenable to genetic analysis. [source]

Uptake of Calcium by Mitochondria: Transport and Possible Function

IUBMB LIFE, Issue 3-5 2001
Thomas E. Gunter
Abstract Vertebrate mitochondria contain a complex system for transport of Ca 2+ and related ions, consisting of two saturable modes of Ca 2+ influx and two separate, saturable mechanisms of Ca 2+ efflux. The characteristics of the mechanisms of Ca 2+ 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 Ca 2+ concentration ([Ca 2+ ] 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 [Ca 2+ ] 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 Ca 2+ efflux and the Ca 2+ -induced mitochondrial permeability transition, which can transport Ca 2+ as well as other ions and molecules and is often considered as a Ca 2+ transport mechanism, are being reviewed separately. [source]