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Biomedical subjects

L Girardier

Publications and source records attributed to L Girardier.

At least 109 records · Page 6Linked to original sources
PubMed1967

Crayfish muscle: permeability to sodium induced by calcium depletion.

Membrane of crayfish muscle fibers becomes selectively permeable to sodium when the calcium concentration of the bathing medium is reduced. Removal of calcium or its reduction below 1 or 2 millimole per liter causes large transient depolarizations up to 70 millivolts in amplitude. They resemble pro longed action potentials and occur only in the presence of sodium. The responses are abolished when tris(hydroxymethyl)aminomethane or lithium is substituted for sodium, and are blocked by tetrodotoxin even in the presence of sodium.

Animals↗
PubMed1965

Correlated morphological and physiological studies on isolated single muscle fibers. I. Fine structure of the crayfish muscle fiber.

Single fibers isolated from walking leg muscles of crayfish have 8- to 10-micro sarcomeres which are divided into A, I, and Z bands. The H zone is poorly defined and no M band is distinguishable. Changes in the width of the I band, accompanied by change in the overlap between thick and thin myofilaments, occur when the length of the sarcomere is changed by stretching or by shortening the fiber. The thick myofilaments (ca. 200 A in diameter) are confined to the A band. The thin myofilaments (ca. 50 A in diameter) are difficult to resolve except in swollen fibers, when they clearly lie between the thick filaments and run to the Z disc. The sarcolemma invaginates at 50 to 200 sites in each sarcomere. The sarcolemmal invaginations (SI) form tubes about 0.2 micro in diameter which run radially into the fiber and have longitudinal side branches. Tubules about 150 A in diameter arise from the SI and from the sarcolemma. The invaginations and tubules are all derived from and are continuous with the plasma membrane, forming the transverse tubular system (TTS), which is analogous with the T system of vertebrate muscle. In the A band region each myofibril is enveloped by a fenestrated membranous covering of sarcoplasmic reticulum (SR). Sacculations of the SR extend over the A-I junctions of the myofibrils, where they make specialized contacts (diads) with the TTS. At the diads the opposing membranes of the TTS and SR are spaced 150 A apart, with a 35-A plate centrally located in the gap. It appears likely that the anion-permselective membrane of the TTS which was described previously is located at the diads, and that this property of the diadic structures therefore may function in excitation-contraction coupling.

Animals↗
PubMedDate not supplied

[Autoregulation of body weight and body composition in man. A systematic approach through models and simulation].

The regulation of body weight and its composition in humans is examined from the standpoint of system analysis. It is based upon the hypothesis that the ultimate purpose for modulating body energy stores is to ensure the maximum duration for survival of the individual in the face of calorie deficit. A mathematical model, which is built on this hypothesis, allows quantitative simulation of variations in body weight and composition which occur during cycles of underfeeding/refeeding, and is achieved with the use of three global parameters. One of them controls the partitioning of body energy stores between fat and lean tissues, and the other two are concerned with the control of adaptive thermogenesis. The first of these two parameters for thermogenesis modulates the efficiency of fat storage by a function which is inversely proportional to the level of replenishment of the adipose tissues, and the other one controls regulatory thermogenesis which is a direct function of energy imbalance. These two forms of adaptive thermogenesis operate independently of each other and their amplitude depends upon the nutritional background of the individual. This model can be used as a theoretical framework for integrating numerous data in the literature on physiological processes that are involved in the regulation of body weight and body composition.

Body Composition↗
PubMedDate not supplied

A role for interferon-gamma in the hypermetabolic response to murine toxoplasmosis.

Toxoplasma gondii (Me49 strain) infection into Swiss Webster mice is followed by hypermetabolism and weight loss in the acute phase lasting 14 days. In the subsequent chronic phase of infection, mice showed either a resolution of hypermetabolism and partial weight recovery (Gainers) or persistent hypermetabolism, with stable weight loss (Non-Gainers). The hypermetabolic response was not associated with an augmentation in the thermogenic uncoupling protein 1 (UCP1) mRNA expression in interscapular brown adipose tissue (BAT), but rather UCP1 expression was reduced. Hypermetabolism is associated with high lipid oxidation as attested by a low respiratory quotient (RQ). Neither BAT nor sympathetic nervous system appear to be involved in the increased lipid utilization, since propranolol did not increase the lower RQ in infected mice. The mitochondrial lipid oxidation blocker mercaptoacetate did not reestablish the respiratory quotient RQ in acute infection (on day 4) and in chronically infected Non-Gainer mice. This suggests an important extra-mitochondrial mechanism of lipid oxidation. Increased lipid peroxidation was detected especially in serum, lung, spleen and liver, which are rich in macrophage-type cells. Following infection peritoneal macrophages exhibited an enhanced capacity to produce reactive oxygen species (ROS). Using IFN-gamma knockout mice we observed that not only the hypermetabolic response was ablated in these mice but there was not a marked increase in ROS production or preferential oxidation/peroxidation of lipids in the acute phase of infection prior to the cachectic phase. The present study described a novel hypermetabolic mechanism involving enhanced lipid peroxidation dependent on IFN-gamma, especially associated with tissues rich in macrophages.

Adipose Tissue, Brown↗